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Grus japonensis, dividedd pen with mound. Click here for full-page view with caption. Grus canadensis. Click here for full-page view with caption. Grus canadensis in divided pen. Click here for full-page view with caption. Grus vipio - group of subadults. Click here for full-page view with caption. Rudimentary nest with egg, in shed. Click here for full-page view with caption. Divided pen with pool at fence line. Click here for full-page view with caption. Sandhill cranes in divided pen. Click here for full-page view with caption. Squeezing the cloaca of a male crane to get a semen sample. Click here for full-page view with caption. Crane semen sample with low sperm count. Click here for full-page view with caption. Crane semen sample with moderate sperm count. Click here for full-page view with caption. Crane semen sample with high sperm count. Click here for full-page view with caption. Crane semen sample with high sperm count. Click here for full-page view with caption. Cryopreservation tank. Click here for full-page view with caption. Cryopreservation tank, open, showing straws. Click here for full-page view with caption. Floodlight for increasing photoperiod. Click here for full-page view with caption. Wooden dummy crane egg. Click here for full-page view with caption.

Introduction and General Information

  • Most people keeping bird collections wish to breed from their birds. In order for birds to breed, they need to be in the correct pairing or grouping, with suitable environmental conditions, including factors such as seclusion/cover and nesting facilities, and with adequate nutrition and water availability. Genetic considerations should not be forgotten.
  • Reproductive failure may result from inappropriate enclosure design, with the lack of suitable nest sites, nest building materials or other appropriate environmental cues. Partial construction of appropriate nest sites, and provision of suitable materials may be vital to initiate breeding.
  • For some species environmental cues such as increased daylength or rainfall may be required to initiate breeding.
  • The presence of an adequate food supply may be important for the initiation of breeding.
  • The presence of extra, unpaired birds may be disruptive to breeding in some species, as the unmated bird attempts to procure a mate.
  • Some individuals show inappropriate behaviour such as egg-eating and infanticide (seen much more commonly in captive birds than in wild individuals), as well as aggression towards other adults and/or chicks which stray into their territory.
  • Nutritional and behavioural stresses, as well as abnormal rearing experiences, may all affect adult parental behaviour.

(J8.17.w1, J54.2.w1, B105.15.w2, P1.1977.w2, V.w5).

Waterfowl Consideration
  • As with other species, good nutrition and a suitable environment are important factors in breeding waterfowl. In general, a higher protein diet should be provided prior to and during the breeding season, soluble grit should be provided and plenty of suitable nest sites, free from disturbance, should be available. Breeding success may be reduced if waterfowl are too fat as well as if nutrition is inadequate.
  • Many gregarious species may be bred successfully in a mixed-species enclosure. However for some species, due to their aggression and territoriality or, conversely, their shyness, breeding results may be better if a breeding pair is kept in their own pen. In the case of timid birds, this is particularly true if the birds are to incubate the eggs and/or rear their young.
  • The commonest causes of poor reproduction are environmental, nutritional or social stress problems (P4.1992.w1).

(B37.x.w1, B29, B40, V.w5).

Crane Consideration
  • Cranes are long-lived, monogamous, territorial breeders, which establish large territories during their breeding season, keeping other cranes out of their territory. Chicks remain with their parents for about 10 months, during which time they pass through a period of sexual imprinting, as well as learning about food, roosting sites, breeding areas and migration routes. Immature and non-breeding individuals form loose flocks through the whole year; when they reach sexual maturity, pairs form life-long bonds and separate from the non-breeding flocks. It is important, for breeding cranes in captivity, to remember these aspects of their behaviour. (J23.17.w5)
  • Cranes are monogamous, and successful pairs may last life-long. (B115.2.w7)
    • A crane which loses its mate with re-pair with another individual. (J23.17.w5) 
  • Cranes are highly territorial when breeding, so visual barriers should be put in place between crane enclosures before the breeding season. (B115.2.w7, P96.1.w1)
    • In captivity, where food is freely available, cranes will breed in quite small areas. However, they are still highly territorial and it is necessary to separate pairs to prevent fighting and the formation of dominance relationships. Visual barriers are needed since visual contact between pairs acts as a distraction and can impede reproduction. (J23.17.w5)
  • General good husbandry, including provision of adequate food and water, is important for breeding. (P1.1980.w8)
  • Nesting material should be provided within the enclosure to stimulate nest building, although nests built in captivity generally will be much more rudimentary than those built by cranes nesting in wetlands in the wild. (B115.2.w7, P1.1980.w8, P96.1.w1)
  • Failures of reproduction may occur for a variety of reasons, including wrong sexing of birds (leading to keeping of two males or two females as a "pair"; incompatibility or imbalance in dominance relationships leading to male and female not forming a strong pair; disturbance by humans, the presence of other cranes, or other species.
  • Vocal contact does not have an adverse effect and may even be stimulatory for cranes in adjacent pens. (J23.17.w5)
  • Cranes do not need wet/marshy conditions for reproduction; in the absence of water, often they will construct only superficial nests. (J23.17.w5)
  • While pairs may nest in a bare enclosure, breeding may be encouraged by the provision of a secluded area (e.g. using vegetation), and by providing a marshy area and/or a shallow stream. (P1.1986.w4)
  • Prior to breeding, even if nest building is not obvious, cranes will become more aggressive and will show preference for a particular part of their enclosure. (J23.17.w5)
  • If egg clutches are removed after they are laid, as many as 12 eggs or even more (17 has been recorded) may be laid (J23.14.w5); laying may be increased if each egg is removed after it is laid, rather than waiting until the second egg of the clutch has been laid. (J23.17.w5)
  • If removing clutches, the risk of the first egg being broken can be reduced by replacing it with a dummy egg until the second egg has been laid. (J23.17.w5)
  • Cranes often can be induced to recycle two or three times if eggs are removed. As many as 18 eggs may be laid by one female in a given year, although lower numbers are more usual (e.g. 6.3 +/- 3 eggs per year for nine greater sandhill cranes (Grus canadensis - Sandhill crane) studied over two years. (J54.2.w1)
  • Pair bonds usually form during the second or third year. It may take as little as a few hours or as long as several months to develop a pair bond. (J23.14.w5)
  • Successful breeding requires the development of socially and sexually compatible pairs. (P1.1980.w8)
  • Both parent-reared and hand-reared cranes may breed successfully. (P1.1986.w4)
  • There is a need for more breeding of cranes in captivity. (N1.80.w1)

Stress and disturbance

  • Stress and disturbance can interfere with reproduction by increasing the birds' corticosterone levels. (J54.2.w1) Measures should be put in place to minimise disturbance during the breeding season. (P1.1980.w8)
  • Cranes may be stressed and distracted from breeding by visual contact with cranes in adjacent enclosure, adjacent predators such as wolves, or human disturbance. (P1.1986.w4)

Moving pens and construction activity

  • Cranes may fail to lay if they are disturbed for example by being moved between pens or by construction activity near their pen during or just prior to the breeding season. (P87.7.w5)
  • Moving cranes between pens (other than to an adjacent pen) may negatively impact on breeding and should be avoided, if possible, in a pair which is breeding. (P87.7.w5)
  • Moving to a different pen may be beneficial if it involves moving the pair to a less disturbed pen. (P87.7.w5)
  • Scheduled construction activity should be timed to start after the moult, when chicks are several months old, and finish well before the start of the breeding season. (P87.7.w5)

Disturbance by personnel

  • Access to breeding areas should be restricted to essential personnel only. (P1.1980.w8, P87.7.w5)
  • Each crane enclosure should have a secure, undisturbed area where birds can nest. (P87.7.w5)
  • Cranes are able to tell people apart. Experienced staff who are familiar to the cranes, and familiar with the cranes and their behaviour are less likely to disturb the birds. (P87.7.w5)
  • Experienced aviculturists may be able to identify potential and actual sources of stress so that management can be adjusted to minimise this stress. (P87.7.w5)
  • Routine husbandry procedures, including cleaning, feeding, checking for eggs and carrying out artificial insemination, should be carried out on a regular, predictable daily schedule. (P1.1980.w8, P87.7.w5)
  • Watering and feeding inside a shelter can help minimise disturbance during routine husbandry (servicing). (P87.7.w5)
  • Regular contact with aviculturists helps to familiarise the birds to these personnel, reducing stress when further contact is required. (P87.7.w5)
  • Wild-caught cranes are most sensitive to disturbance; parent-reared birds also can be very nervous. (P87.7.w5)
    • Condition wild-caught birds to the presence of people gradually. (P87.7.w5)
      • Feeding with treats, initially by throwing the treats while standing on the other side of, and at a distance from, the enclosure fence, progressing to feeding just the otehr side of the fence, and then to feeding at closer and closer distances while inside the enclosure, may be useful to condition a wild-caught crane to accept human presence. (N31.40.w1)
    • Expose parent-reared chicks to humans from a young age to minimise inhibition of breeding later. (P87.7.w5)
    • Encourage the expression of dominant behaviour towards people. (P87.7.w5)
    • Aviculturists (keepers) should assume submissive postures when working around these birds, avoid eye contact, and make soft sounds to let the birds know they are approaching. (P87.7.w5)
    • Offer small amounts of treat foods (e.g. whole corn (maize)) daily to improve tameness. (P87.7.w5)

Public display

  • In general, cranes which are on public display are likely to lay fewer eggs than those which are maintained off display. (P87.7.w5)
  • Hand-reared cranes are more likely to breed readily while on public display than are parent-reared or wild-caught individuals. (P87.7.w5)
  • If cranes are on public display, breeding may be improved if keeper activities occur at the same end of the pen as the area accessible to the public, leaving the far end of the pen undisturbed by human activity. (P87.7.w5)
  • Cranes may fail to lay if they do not feel they have a secure part of their enclosure; this is most likely to occur with birds on public display. Care should be taken to carry out husbandry activities from the same part of the enclosure as the public have access to, so that the far end is undisturbed. (P87.7.w5)
    • Consider placing visual barriers around part or even all of the enclosure during the breeding season. Signs should be placed around the enclosure explaining to the public the need for the barriers to give the birds necessary privacy for breeding. (V.w5)
    • Bushes, shrubs or even conifers (with thick branches at and below crane eye level) may be planted around part of the enclosure perimeter to act as a stand-off barrier (if outside the enclosure) and give visual seclusion. (V.w5)
    • Planting within the enclosure can improve seclusion but will make the cranes less visible; a trade-off may be needed and signs should explain the birds' need for privacy for breeding. (V.w5)
Intraspecific interactions
  • Cranes are highly territorial; they breed best in isolated enclosures. (P87.7.w5)
  • Breeding may be inhibited by the presence of other cranes in adjacent pens, due to compromised territorial security and males spending excessive amounts of time aggressively displaying to adjacent cranes to the extent that normal pair interactions are inhibited. (P87.7.w5)
    • Provide buffer zones or visual barriers between enclosures. (P87.7.w5)
      • Visual barriers may be important for nervous, easily-disturbed pairs. (P1.1980.w8)
    • For a breeding unit, a line of pens should be constructed with each pair having alternate-year use of two adjacent pens. Each pair has an empty pen on either side of its own enclosure, giving an effective visual territory three times the size of the enclosure it is occupying. (P1.1980.w8, P87.7.w5)
      • A gap of at least nine metres should be left as a "buffer zone" between rows of such pens. (P87.7.w5)
    • Observe carefully when cranes are moved so that pairs are new neighbours. (P87.7.w5)
    • Note: males may be stimulated to high levels of aggression by visual contact with adjacent cranes; this can lead to displacement of the aggression onto the bird's mate, which can be fatal. If the female is observed showing excessive submissive behaviour, it may be necessary to separate the pair temporarily into adjacent pens to avoid the female being injured or killed. (P87.7.w5)
Published Guidelines linked in Wildpro
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Genetic Considerations and Breeding Programmes

Alongside efforts to preserve endangered species as self-sustaining wild populations, captive populations may be vital to ensure survival of some species and for preservation of genetic diversity. (B115.9.w13)
  • Genetic diversity is important; genetic variation within a population is the basis for change within a population, allowing adaptation, and in an individual, the degree of heterozygosity and avoiding homozygosity of deleterious genes is important to maintain fitness (survival and fertility). (J23.17.w8, J23.27.w3, J54.5.w1)

Breeding programme aims and priorities

Breeding programmes in zoos may be to develop and maintain self-sustaining captive populations to allow continued exhibit of the species, or to conserve species or gene pools whose continued existence in the wild is doubtful. (P97.1.w34) Priorities of breeding programmes vary depending on the starting population and the aim of the programme:

  • In species with very few founders, breeding programmes should aim to maximise reproduction, expanding the size of the population as rapidly as possible. (J23.27.w3)
    • This reduces loss of genetic diversity and minimises the risk of genetic loss through founders not breeding, or through loss of the population due to disease, accident, a distorted sex ratio, a small number of non-breeding females etc. (J23.27.w3)
      • Populations numbering less than 50 (or even 100) are particularly vulnerable to crashes due to disease, distorted sex ratio, natural disasters etc. (J23.27.w3)
  • For short-term captive breeding prior to reintroduction. (J54.5.w2)
    • Rapid breeding of as many offspring as possible is required. The captive population ideally should be held in an environment similar to the natural environment (or similar to the environment into which the birds will be released). (J54.5.w2)
    • Selection should be used only to select against outliers, reducing the genetic load [of deleterious alleles]. (J54.5.w2)
  • For long-term management of endangered species in captivity. (J54.5.w2)
    • The aims are to maintain a viable population, preserve as much as possible of the genetic variation, and preserve the option for future reintroduction. (J54.5.w2)
    • Management should aim to equalise founder representation and maximise effective population size. (J54.5.w2)
    • Selection may be required to control the genetic load. Culling to achieve this may be in conflict with maintaining equal representation of founders; culling of outliers may be delayed until the population size has grown, to ensure that the genetic loss from the culling is not greater than the genetic gain from removal of outliers. (J54.5.w2)
    • It may be necessary to allow some adaptation to captivity (e.g. improved survival and breeding) but this should be minimised, limited only to what is essential for the captive population to survive. Some inadvertent selection for adaptation to captive conditions may be inevitable. (J54.5.w2) 
    • Selection for genetic diversity should not be carried out; genetic diversity should be maintained by maximising the effective population size and maintaining equal representation of founders. (J54.5.w2)
    • It has been suggested that captive breeding programmes should aim to retain 90% of the average heterozygosity of the founders for 200 years. (J54.5.w1)
    • Maintenance of as much as possible of the genetic variability present in the wild gene pool requires both deliberate avoidance of inbreeding and demographic management of the population to establish and maintain a stable population. (P97.1.w34)
    • Variables to be considered include: the number of generations over which it may be necessary to maintain the captive population, the age and sex composition of the breeding population, age-specific and sex-specific fecundity and survivorship, the size of stable population required (based on known life history features), the carrying capacity of zoos for the species, requirements for surplus individuals and how practical it is to develop controlled breeding or mating. (P97.1.w34)
    • Accurate record keeping is required. (P97.1.w34)
    • A breeding policy needs to be explicitly formulated and agreed by all parties concerned. (P97.1.w34)
    • Animals need to be of known origin, with pedigrees preferably traceable back to the original wild population. (P97.1.w34)
    • The age and sex structure should be defined, and the number of animals preferably should be chosen based on the breeding strategy.
    • "Explicit definitions of the need for introduction of new wild stock should be made in terms of breeding strategy and breeding management programs with a view to maintain some defined level of genetic variability in the population." (P97.1.w34)
    • Data collection and data sharing are vital; ISIS can provide census and vital statistic data, demographic projections, pedigrees, studbooks, and data for analysis of breeding relationships including calculation of inbreeding coefficients. (P97.1.w34)
    • For a maximally efficient genetic management programme, it is important to remember that the effective population size will determine the rate of loss of genetic diversity per generation. Given the use of a maximum avoidance of inbreeding scheme, the size of the effective, rather than the actual, population, depends on equal contribution by all members of the population to the next generation, i.e. equal family sizes, and an equal number of males and females breeding - for species where social organisation does not match this, management (e.g. rotation of breeding males) is required. (P97.1.w34)
      • The tendency to favour individuals which do well and breed well in captivity must be avoided to avoid selection of captive-adapted, inbred strains. (P97.1.w34)
      • From a given pairing, selection of offspring to contribute to the next generation must be randomized, avoiding selection based on unconscious preferences. (P97.1.w34)
  • Where the aim is to maintain populations purely for education/exhibition, selection should be used to control the genetic load. Selection can be used also to select for classic phenotypes, ensuring animals on display are representative of the typical wild form. Moderate selection for easy management and maintenance (e.g. tameness, willingness to breed in captivity, adaptation to inexpensive readily available diets) may be useful. (J54.5.w2)
    • However, species considered common may change in conservation status, so that captive populations may become of conservation importance in the future. (J54.5.w2)
    • Selection of zoo-domesticated stock probably would result in unrepresentative animals not suitable for life history studies or for development of data suitable for use in managing the species in the wild. (P97.1.w34)
    • Zoo-domesticated, inbred strains would be at high risk of loss of vigour, viability, growth rate and fertility, and could therefore become extinct. (P97.1.w34)

Preserving genetic diversity and avoiding inbreeding

  • As a general rule, inbreeding is to be avoided. Inbreeding occurs inevitably when the population is very limited in size, as may be the case for endangered species. In these circumstances, studbooks may be kept and pairings made to minimise inbreeding. Some species are known to have fallen to very low numbers and recovered without any indications of problems arising from inbreeding. In others, infertility, poor hatchability and poor survival have been noted and thought to be related to inbreeding. 
  • Inbreeding is used in aviculture in a controlled manner when breeding to "fix" a particular characteristic, such as an unusual colouration of plumage. When used for this purpose (which is not appropriate for conservation purposes) the risks of also enhancing undesirable characteristics should always be considered.
  • In a few species, populations have descended from only a few individuals without any apparent deleterious effects (e.g. Laysan teal, Pere David's deer), however these should be taken to be the exception rather than the norm. (J23.17.w7) However, in general, inbreeding results in inbreeding depression with reduced fertility, fecundity, lactation, viability, growth rate etc. (J23.17.w8)
    • Inbreeding depression leading to reduced fertility can quickly cause a small population to become extinct. (J23.17.w8)
    • Inbreeding depression may be more likely to arise with animals which were previously outbred rather than those with high natural inbreeding. (B482.3.w3)
    • In captivity, the effects of inbreeding may be compounded by management of breeding to ensure that different founders provide equal genetic contributions, and by the lack of the reproductive competition and associated social stimulation which generally occurs in the wild. (B482.3.w3)
  • "Maximum avoidance of inbreeding" can be carried out by, in each generation, mating the least-related individuals with each other. For a captive population of about 50-100 individuals, this should preserve about 50% of the original genetic diversity over 100 generations. (J23.17.w8)
  • The population should be expanded to carrying capacity as fast as possible, while breeding all available animals and ensuring equal family sizes. (J23.17.w8)
  • As well being advantageous to reduce inbreeding, managing for equal family sizes slows the rate of unintentional domestication which may occur from greater breeding of less aggressive, easier to handle, more readily breeding individuals. (J23.17.w8)
  • Genetic diversity is greatest when a 1:1 male: female ratio of breeding individuals is maintained. Where the actual ratio of breeding animals is fare removed from this, e.g. if social criteria require one male with several females, the males should be rotated to equalise their breeding potential. (J23.17.w8)
  • Genetic strategies and demographic management should be coordinated. (J23.17.w8)
  • For maximum preservation of genetic diversity over time, generation time should be maximised, since there is the opportunity for loss of genetic variation at each generation. (J54.5.w1)
  • To minimise loss of genetic diversity in a captive population, breeding programmes should:
    • Involve an adequate number of wild-caught founders. (J54.3.w2)
      • For both conservation and reintroduction purposes, the founder population should be as large as possible with an approximately even sex ratio. (J23.17.w8)
      • To maintain 90% of genetic diversity over a period of 200 years, a minimum of 20 effective individuals, and preferably at least 25-30 is generally required. (J54.5.w1)
        • If there are 20-30 effective founders, average heterozygosity will be preserved. To preserve rare alleles from the wild population, 30-50 effective founders are required. (J23.27.w3)
      • If even one effective founder from the wild population enters the captive population each generation, this can be sufficient to keep the captive population representative of the wild gene pool. (J23.27.w3)
    • Equalise, as much as possible, the genetic contribution of the founders to the population. (J23.17.w8, J54.3.w2)
    • It is preferable for genetic purposes to maintain an even sex ratio of animals contributing to each generation, and for all the members of one generation to contribute equally to the next breeding generation (i.e. for an equal number of offspring to be produced and used for breeding). (J23.17.w8)
      • This minimises inbreeding and decreases the risk of domestication which may arise from the individuals which breed most easily in a captive situation becoming over-represented in the breeding stock. (J23.17.w8)
    • Specify matings to minimise inbreeding. (J54.3.w2)
    • Ideally, animals who are least related to one another are mated - a process known as "maximum avoidance of inbreeding." If this is used in each generation, then with a starting population of 50-100 animals it would be possible to preserve over half of the genetic diversity of the original population over 100 generations. (J23.17.w8)
    • Maximise the effective population size, by manipulating the number of offspring per parent, and the sex ratio of the population. (J54.3.w2)
      • The effective population size is largest when each individual parent produces the same number of progeny. (J23.27.w3***(CHECK THIS, J407.17.w1)
    • Maintain a demographically stable population. (J54.3.w2)
  • To maximise genetic diversity: (B115.9.w13)
    • The population should be started with an adequate number of founders (at least 20 effective i.e. reproducing founders).
    • The population should be expanded to carrying capacity as fast as possible; this capacity must be larger than the minimum viable population size.
    • The sex ratio should be equalised.
    • Family size should be equalised (in each generation, breeding individuals should produce equal numbers of offspring to contribute to the next breeding generation).
    • Once carrying capacity is reached, the size and growth of the population should be stabilised, avoiding population size fluctuations.
    • Once carrying capacity is reached, the population should be managed for longer generation times.
    • Inbreeding should always be minimised.
    • Always manage for a stable age structure.
    • (B115.9.w13)
    • To properly use a computer-based demographic programme a model for each species must be developed based on: (P97.1.w34)
      •  Estimate of the carrying capacity of the captive breeding groups.
      • The need for surplus individuals (for exhibit in non-breeding institutions, use in research programmes etc.)
      • Determined or estimated fecundity and survivorship by age and sex classes. In particular, for relatively long-lived species, adequate first-year survivorship and average annual adult survivorship data are required, in order to determine the average number of offspring required per parent to maintain a stable population size.
        • It is essential that mortality data are recorded accurately, for survivorship data and for detection of detrimental inbreeding effects.
      • The known age and sex structure of the existing population. This is used with survivorship and fertility data to predict the demographic structure of the population.
      • An explicit plan for moving from the current to the desired stable population must be devised, tested and agreed on. This should be examined and stochastic models used to predict possible fluctuations.
      • Note: similar modelling and projections can be used to formulate a strategy for planned reintroduction projects. (P97.1.w34)
    • A deliberate breeding plan can more effectively preserve the maximum heterozygosity than can random breeding. (P97.1.w34)

Use of reproductive technology in maintaining genetic diversity

  • Semen collection and cryopreservation can help in the maintenance of genetic diversity by increasing the number of potential founders (collecting semen from wild or captive individuals that, for whatever reason, have not contributed genetically to the captive population, or are underrepresented genetically in the population), and, via cryopreservation, extending the reproductive life of those founders and their closest descendents. (J54.3.w2)
    • Collection and preservation of semen from founders does not allow preservation of genetic material from female founders. However, collection of semen from male offspring of female founders (particularly those genetically underrepresented in the population) does allow some preservation of their genetic material. (J54.3.w2)
    • Ideally, F1 offspring should be produced from different pairings (male A with female B and male C with female D, but also e.g. male A with female D and male B with female D), to allow separate management of the genetic contributions from different founder individuals. (J54.3.w2)
    • Since each F1 individual can have inherited only part of the allelic diversity of each parent, for maximum probability of representation of all the allelic diversity of the founders, semen should be collected from several (ideally six to nine) F1 offspring of given founders. (J54.3.w2)
    • In the absence of founders or their F1 descendents, semen should be collected and stored from individuals with genomes least exposed to genetic drift and inbreeding, and within these individuals, particularly from descendents of genetically underrepresented founders. (J54.3.w2)
      • Careful analysis of pedigrees and calculation of inbreeding coefficients and the relative genetic contribution of each founder is required. (J54.3.w2)
    • For further information on semen collection and cryopreservation see: Artificial Insemination.

Demographic management

Demographic management is an important part of the management of captive populations, alongside genetic and behavioural management. (J23.17.w9)

  • A demographic model needs to consider the required population size, as indicated by carrying capacity and any need to provide surplus individuals for other purposes. (J23.17.w9)
  • The demographic part of a management plan should specify the number, ages and (in part) sexes of individuals to be retained in the breeding population and will indicate how many progeny need to be produced within a given time interval, and specify the number and ages of animals to be bred.
    • Exactly which individuals within a given sex and age class should breed will depend on genetic management.
    • Behavioural management will indicate the grouping and movement of animals (e.g. rotation of males where behavioural grouping requires uneven sex ratios of breeding groups).

    (J23.17.w9)

  • Usually, demographic management aims to produce a stationary (stable) population, with a constant population size and stable age distribution. (J23.17.w9)
    • A stable population is advantageous because it minimises the risk of demographic disaster due to random fluctuations or unpredicted developments in population.
    • Production and maintenance of a stable population involves manipulation of potential survivorships (by removing individuals from the population) and potential fertilities (by limiting breeding).
      • Animals removed from the breeding population would be available for other uses. 

    (J23.17.w9)

  • Application of demographic models to assist long-term captive management and possible reintroduction would require: (J23.17.w9)
    • Determining of the existing and, if possible, the potential age- and sex-specific survivorships and fertilities of the population; calculation of the existing age/sex structure.
    • Calculation near-future changes in the population size and age structure, subject to the survivorships and fertilities determined above.
    • Determining the finite rates of change and stable age distribution associated with the determined sets of existing and potential survivorships and fertilities.
    • Determining, as closely as possible (a) the carrying capacity for the captive population; (b) the number of surplus animals needed for other purposes (e.g. reintroduction programmes).
    • Within the upper limits set by the potential or maximum existing values of survivorships and fertilities, constructing (computer-aided) the one or more sets of managed survivorships and fertilities which, by varying amounts of culling (removal of individuals from the managed population) and/or breeding restriction, will produce a stationary captive population. 
    • Determining the sets of stationary age distributions associated with each of the calculated stationary sets of managed survivorships and fertilities. The total number of animals in one or more of these sets should be approximately equal to the desired carrying capacity for the population
    • With computer-assistance, devise a plan for moving from the existing population to a stationary population which best fits the carrying capacity and surplus population desired.
    • Selecting individual animals for demographic manipulation in accordance with genetic models.
    • N.B. It would also be necessary to consider stochastic (random or chance) population fluctuations that might occur in the future.

    (J23.17.w9)

Production of birds for reintroduction programmes

  • The needs of reintroduction programmes are different from those of long-term captive management. Rather than maximising generation time, there is a need for large numbers of birds to be hatched and reared.
Waterfowl Consideration
  • Whenever possible, pairs should be formed from unrelated birds. Continual inbreeding may lead to inbreeding depression with detrimental results such as infertility and weak ducklings.
  • Unrelated pairs may be more likely if the two birds are acquired from different collections. Alternately, two young pairs (of possibly-related birds) may be procured, one from each of two different collections, then split up and reformed.

Records:

  • Records should be kept for each female including the identity of her partner, the date the first egg in each clutch is laid, the laying site chosen, the date the eggs are set, hatching dates and details of fertility and hatching success.

(B29, B40, V.w5).

Crane Consideration
  • Genetic management and breeding programmes are important for captive crane populations. Of the 15 species of cranes, 11 are IUCN red-listed (2006) in the categories Critically Endangered (one), Endangered (three) or Vulnerable (seven). (W2) Within the remaining five species with are oevrall considered "Least Concern", some subspecies are nevertheless at risk. 
  • For most species of cranes, breeding and rearing are not now considered particularly difficult. (P91.1.w1) Cranes are long lived and with modern techniques including egg-pulling and hand-rearing, several chicks per year can be produced from a single fertile pair. Where fertility is poor, it can be improved by the use of artificial insemination (see below: Artificial Insemination)
  • Captive breeding programmes are important to ensure that genetically viable, self-sustaining captive populations of cranes are developed, to safeguard species against extinction and that, if birds are eventually released in reintroduction programmes, they are genetically representative of the original wild founders. (P91.1.w1) Management of captive crane populations is important to ensure preservation of genetic diversity. (P91.1.w1) Because crane pairs can be long lived, a good breeding pair can produce large numbers of offspring. In a situation where other pairs are breeding much less well, the offspring from fecund pairs can make up a large proportion of the population (J23.27.w2)
  • Modern techniques for general husbandry, sexing and pairing, artificial insemination, incubation, hatching assistance and rearing of chicks allows the possibility of a greatly increased production of crane chicks. However, the regional or even world-wide founder base is relatively narrow for several species. Additionally, in several species certain pairs have bred well and their genetic lines have become relatively over-represented, and even inbred, while other potential founders are underrepresented or have not bred. (J23.27.w2)
  • Multiple-clutching (removal of eggs for artificial incubation to stimulate production of more eggs) may be useful for species with low numbers of founders, to rapidly expand the population. (P1.1986.w4)
  • Cranes need a relatively large amount of space (J23.27.w2) The total number of "crane spaces" (i.e. suitable enclosures) in zoos, bird gardens and specialist breeding collections is limited. (J23.27.w2, J54.14.w2) Available space at present is being used not only for species which are of conservation importance but also for non-threatened species. For the long-term, captive management of cranes requires genetic management, breeding management and careful use of available resources. (J23.27.w2)
  • When breeding programmes require a particular genetic pairing and this is impractical, due to logistics, or it is undesirable to risk stopping a female from egg-laying by splitting her from her present mate, artificial insemination can be used. (P17.43.w1, V.w5)
  • Collections holding and exhibiting cranes generally will wish also to breed them regularly if possible. This may run counter to recommendations for genetic management. (J23.27.w2)
  • The potential longevity and long breeding life of cranes provides both advantages and potential problems. (J23.27.w2)
    • To maximise generation time, breeding should be postponed for as long as possible, however this risks losing genetic material if the birds die before they breed. (J23.27.w2) Therefore it may be preferable to encourage breeding of birds early initially, to provide e.g. four offspring, then wait some years before breeding them again.
    • By multiple-clutching, artificial (or foster) incubation and hand-rearing, a large number of chicks can be produced. (J23.27.w2) This could be useful for rapid population expansion to decrease genetic loss.
  • It has been suggested that for species such as Grus vipio - White-naped crane in managed programmes, perhaps two chicks should be hatched and reared initially (e.g. when the pair was three to five years old) to ensure that they were fertile and that their genes were represented, then further breeding would not be carried out for about three to five years (or earlier if the offspring died). For ideal genetic management, the older offspring would be removed from the population as younger birds were bred, to increase generation time and reduce the problems of over-production. (J23.27.w2)
  • Cranes which are surplus to requirements genetically could be held in non-breeding situations (e.g. in mixed-species exhibits) or in collections outside management breeding programmes, for example collections owned by reputable private individuals. So long as individual cranes can be permanently identified (see: Bird Identification), this keeps open the possibility of calling such birds back into the breeding programme if required, for example due to unexpected deaths of related breeding-programme individuals. (J23.27.w2, V.w5)
  • Genetic management requires detailed records of the history of each crane; this is generally contained in studbooks, which may be regional or international in scope. (P91.1.w1)
    • Increasingly, international cooperation in studbook management is required. (P91.1.w1)
  • Once the required information has been gathered into a studbook, genetic and demographic analysis is needed, followed by development of a plan (e.g. SSP) for management of the species. (P91.1.w1)
  • Note: high levels of cooperation are required if management plans are to succeed. Decisions and requests made as determined by the plan may require a given institution to stop breeding a prolific pair, or to send a favourite bird to another collection. (P91.1.w1)
  • Artificial selection, and particularly selection of cranes adapted for captivity (e.g. greater productivity of tame individuals) should be avoided. (B115.9.w13)
  • For cranes, the captive "carrying capacity" is about (per species) 100-500. (B115.9.w13)

Genetic management

  • The first priority is to ensure reproduction from as many founders as possible. (B115.9.w13)
  • The second priority is to maximise the number of offspring per founder. (B115.9.w13)
  • The population must be increased as rapidly as possible to increase the chance of survival. (B115.9.w13)
    • However, it can be genetically harmful for the genetic representation to be highly skewed in favour of a small number of founders. (B115.9.w13)
    • Growth rate fluctuations should be avoided if possible; these can unbalance the age distribution and this can decrease the stability of the population. (B115.9.w13)
    • The size of the minimum viable population must be calculated using appropriate software. (B115.9.w13)
  • If the population is large enough to be out of danger of extinction, genetic management should be carried out to equalise the genetic representation of the founders. (B115.9.w13) 
    • This can be carried out by increasing the number off offspring from poorly represented pairs. (B115.9.w13)
    • For highly represented pairs it may be necessary to cease breeding or remove offspring from the managed population (by euthanasia, or by dispersal outside the managed population). (B115.9.w13)

Demographic management

  • The population should be manipulated to produce a stable age structure and a stable population size, close to carrying capacity. (B115.9.w13)
  • Demographic analysis by mathematical models, using in particular age-specific fertility and age-specific mortality, but also age at first reproduction, longevity, reproductive life span and sex ratio, can indicate the number of offspring required per breeding pair over their lifetime; this can then be used to calculate annual breeding objectives. (B115.9.w13)
  • Idially, the sex ratio in the population should be even. However, uneven sex ratios have occurred in captive crane populations (e.g. excess of female Grus japonensis - Red-crowned crane and of male Grus leucogeranus - Siberian crane in North America. This is probably an artefact related to the small sizes of the populations. (B115.9.w13)
  • The rate of loss of genetic diversity can be reduced by increasing generation time, i.e. increasing the average age at which each individual reproduces). (B115.9.w13)
    • For crane populations which are at or near carrying capacity, it may be advisable to allow each pair to breed once or twice soon after reaching sexual maturity, ensuring that they can and do reproduce and pass on thier genetic information. After this, reproduction may be allowed only every five years, until the required number of offspring have been produced. (B115.9.w13)
      • On average, 98.4% of each parent's genetic information can be retained into the next generation by production of six offspring. (B115.9.w13)
    • Alternatives are to delay reproduction or to cull older offspring and breed from younger offspring. (B115.9.w13)

Role of studbooks

Cooperative management programmes

  • No single institution can or should try to establish and maintain a viable captive population of any species; development of cooperative captive crane management programmes is a critical part of recovery strategies. (B115.9.w13, P91.1.w1)
  • Because of the limited space available for cranes in zoos and other institutions, there is a need to coordinate programmes for different crane species.
  • Both regional and world-wide coordination is required. (B115.9.w13)
    • Depending on the species and the number and genetics of individuals in the captive population, it may be advantageous in genetic terms to manage all available individuals worldwide as one population as far as practical (e.g. if only a few birds are held worldwide), or to maintain several separate captive gene pools. (J23.27.w2)

Red-crowned cranes:

Analysis of the red-crowned crane population indicated that of a population of 113 birds (51.54.w8), there were a maximum of 53 (25.28) unrelated birds, but it was probable some of these were related. Of the possible 53 genetic lines, 28 (11.17) had living offspring at the start of 1981. Of the 63 cranes in the most recent generation, 34 were from the three most productive males and 33 from the four most productive females - i.e. about half the generation was produced by only 1/8 of the possible male stocks and 1/7 of the possible female stocks - a very unequal distribution of founders. Additionally, seven of the 25 breeding pairs were related and for five of the pairs the coefficient of inbreeding (.f) would be 0.25 (as of sister:brother or parent:offspring mating) and a further two would have progeny with a .f of 0.125. (P92.1.w2)

The following management plan was suggested in 1983: (P92.1.w2)

  1. "Prevent good breeding pairs from producing too many offspring.
  2. Prevent some of the offspring of overproducing pairs from mating.
  3. Try to breed the stocks that have not yet been bred in captivity.
  4. Develop a mating scheme for all the breeding birds to minimize inbreeding.
  5. Coordinate these measures with a long-range demographic plan that defines the maximum number of Red-crowned cranes that can be kept in captivity, the optimum number of offspring per pair, and related parameters."

(P92.1.w2)

The plan would aim to equalise the number of offspring from each pair. An additional goal was to increase the number of red-crowned cranes in the population, but it was noted that this must be controlled to avoid later inbreeding. (P92.1.w2)

It was noted that: (P92.1.w2)

  • Removing birds from the breeding population could increase the effective population size by nearly 50%.
    • It might be difficult to accept the necessity not to allow productive cranes to breed, but this could significantly increase the genetic diversity of the population 
  • Non-breeding birds could be loaned to zoos wising to display, but not to breed these cranes.
  • Any red-crowned cranes brought into the wild and having to be kept in captivity due to injury should be bred (using artificial insemination if necessary).
  • The world population should be managed as a whole
  • Carrying capacity could be increased by zoos expanding their crane propagation programmes and by cooperation with private aviculturists.
  • An optimum number of offspring per pair should be agreed to maintain a stable population size, close to carrying capacity and maximising genetic diversity while avoiding overcrowding.
  • Many birds would need to be transferred between collections to avoid inbreeding, although cryogenic preservation of sperm might be able to reduce the need for transfers.

(P92.1.w2)

Production of cranes for reintroduction programmes

  • This requires rapid expansion of populations so that large numbers of young can be produced and reared for release efforts. (P91.1.w1)
Associated techniques linked from Wildpro

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Determining Sex

If birds are to be paired for breeding, it is extremely important to correctly identify a male and a female to place together; this is particularly important in breeding programmes for endangered species. (J23.18.w6, J54.25.w3) In some species, it is advantageous to keep one male with several females; again it is necessary to be able to tell the sexes apart. In colony breeding birds this may be less vital, but is still preferred to ensure an appropriate sex balance for behavioural and genetic reasons. 

Pairing two birds of the same sex is a common reason for failure of reproduction. (B13.29.w8, J23.17.w6)

Visual - colour
  • Some birds are sexually dimorphic: the adult male and female can easily be distinguished from one another visually by characteristics such as plumage colouration, iris colour, bill characteristics etc. (B13.29.w8, J23.18.w6)
  • In most dimorphic species, immature birds have characteristics similar to those of adult females. (B13.29.w8)
  • However, in many other species, males and females have similar colouration (are monomorphic). (B13.29.w8, J23.18.w6, J54.25.w3)
Morphometrics - size
  • In some species it is possible to distinguish males and females on the basis of size - weight and/or linear measurements, generally by combining several measurements in a discriminant analysis, although there is often some overlap. (J48.68.w1, J54.10.w5)
  • In birds of prey, females generally are about 1/3 larger than males. However, there is some size overlap. (B13.29.w8)
  • In most bird species, males are generally larger and heavier than females. They may have a larger head, and the bill may have greater length, breadth and depth. In some species this may be visually obvious; in others measuring with calipers may be required. (B13.29.w8)
  • During and just after the breeding season it may be possible to dstinguish between egg-laying females and their mates on the basis of larger vent size in the females (due to recent passage of eggs). (J50.104.w1)
Voice, Display and Behaviour
  • Behaviour can sometimes be used to distinguish male from females. In general, males are more aggressive and play a larger role in territory defence (if applicable) (B13.29.w8)
    • If birds form a homosexual pair, one may take the behaviourally female role and the other the male role. (B13.29.w8)
  • In some species, such as finches, canaries and cockatiels, there are obvious vocal differences. (B13.29.w8)
Vent sexing
  • Vent sexing can be used reliably in some species (anseriformes, most galliformes, ratites, some cracids) by finding the phallus of males on the wall of the cloaca. (B13.29.w8)
  • In columbiformes and passeriformes, there is no phallus but there are prominent papillae of the ductus deferens; vent sexing of these species requires general anaesthesia and a cloacal protractor to allow visualisation of these papillae. (B13.29.w8)
  • There is a risk of injury, even fatal injury, to the bird if this procedure is carried out by inexperienced personnel. (J23.16.w7)
Faecal steroid sexing
  • This may be used by measuring oestrogen and testosterone in faecal samples using radioimmunoassay and calculating the oestrogen/testosterone ratio, which is higher in females than in males. (J23.17.w6)
  • It is necessary to be certain which faecal sample comes from which bird; housing the birds separately while samples are collected avoids error. (J23.17.w6)
  • For small birds, several faecal samples may need to be pooled to provide a larger size sample for testing. (J23.17.w6)
  • The oestrogen/testosterone ratio can provide a reliable sex identification in about 90% of individuals, at least in adults. (J23.19.w4)
  • Additionally, the testosterone concentration is low in females and can indicate sex regardless of the oestrogen/testosterone ratio. (J23.19.w4)
  • Faecal samples for steroid testing should be tested immediately or frozen and stored at -20 C (J23.19.w4) or preferably -40 C. (B115.11C.w12)
Genetic sexing
  • In birds, unlike mammals, females are heterogametic (ZW) and males are homogametic (ZZ). (B13.29.w8, J23.14.w5)
Karyotyping or chromosomal sexing
  • Karyotyping involves analysis of chromosome pairs. Chromosomes can be visualised under the microscope in cells undergoing mitosis (cells in metaphase) and are analysed directly or from photographs. In male birds paired ZZ chromosomes are found; in females, only one Z chromosome is present, plus a small W chromosome. (J3.125.w2, J5.31.w7)
    • Feather pulp tissue can be used as a source of cells. Mitotic cells are found in the tissue from the base of a growing feather. (J3.125.w2, J5.31.w7)
    • Examination can be carried out directly on tissue from cells reaching the laboratory within an hour after collection from the bird. If a longer time has elapsed, cells will no longer by growing and short term culture (2-3 days) is used to induce cells to enter mitosis. (J3.125.w2)
    • A good quality chromosome spread preparation is important. (J5.31.w7, J23.16.w7)
    • The person carrying out the analysis needs to be familiar with the chromosomes of the species group being examined. (J23.16.w7)
  • Karyotyping can be carried out on birds of any age. (J23.14.w5)

Blood

  • Blood cells are cultured, centrifuged, treated with a hypotonic solution, stained and the preparation is photographed. (J5.31.w7, J23.14.w5)

Feather Pulp

  • Growing feathers are required for karyotyping. In small birds a wing or tail feather is needed to provide sufficient material. In growing chicks, all feathers will be growing. In adults, unless the bird is in moult (i.e. with growing feathers) it is necessary to pluck a wing feather or tail feather, then wait (usually two to three weeks, sometimes longer, depending on the species), for the replacement pin feather to become available. This is then plucked to provide the required material. (J3.125.w2, J23.16.w7)
    • A pin feather which is just beginning to protruce from the follicle is ideal, as the rate of mitotic division is high. (J23.16.w7)
    • Care must be taken not to twist or snap the feather shaft. It can be difficult to stop haemorrhage from a broken shaft. (J23.16.w7)
  • For transport to the laboratory, the growing feather is placed into a container with sterile phosphate buffered saline containing 100 iu/mL penicillin, 100 g/mL streptomicin and 2.5 g/mL Amphotericin B. (J3.125.w2)
DNA Probe
  • Birds can be sexed using a DNA probe to a conserved gene on the avian sex chromosomes (Z and W) and Restriction Fragment Length Polymorphism (RFLP). This can be used on a small amount of genomic DNA e.g. from a small blood sample. (P4.1990.w)
  • Various genetic markers on the avian sex chromosomes have been used to sex birds using molecular methods. (J54.25.w3)
  • The first avian W chromosome to be discovered was the chromobox-helicase-DNA-binding gene (CHD-W), which is highly conserved, so that a single set of PCR primers can be used to sex all birds except ratites. There is also a CHD gene on the Z chromosome, but methods have been developed to distinguish the two genes by using restriction enzyme sites present on only one of the two CHD genes to give products of different lengths. (J9.375.w1, J312.16.w2, J335.7.w1)
  • A DNA probe using a single set of DNA primers has been developed which amplifies homologous sections of the CHD-W and CHD-Z genes but incorporates introns whose length usually differs, resulting in a single CHD-Z band on the finished gel for males but two separate bands, representing CHD-Z and CHD-W, for females. (J335.7.w1)
  • A recent development is preparation of genomic DNA from a cut feather including the rachis. This removes the need to collect blood or pluck a feather, reducing stress associated with sample collection. (J54.25.w3)
Genome Size
  • The total DNA content of erythrocytes can be measured. The Z chromosome is larger than the W chromosome, therefore the total DNA content of the cell is larger for males than for females. (J13.61.w2, J48.64.w1, B115.11C.w12)
    • A flow cytometric method has been developed requiring very small blood samples. Used on three psittacines, it was found to be 100% reliable for budgerigars and 94.4% for Amazon parrots but only 51.3% of cockatiels were sexed correctly, suggesting possible within-species variability due to e.g. polyploidy or chromosome mutations. It was also found that measured DNA concentrations varied depending whether blood was tested when fresh or after storage for 48 or 72 hours, and that it sometimes varied to different extents for males and females. (J13.61.w2)
    • A spectrofluorometric method has been developed using a small blood sample (drop) mixed with normal saline and labelled with the fluorochrome 4,6-diamindine-2-phenylindole (DAPI), which binds to the major groove of the DNA double helix. The amount of DNA can be determined by quantification of the emission of fluorescent light at 475 nm when subjected to radiation of 325 nm. The amount of DNA measured in cells of female birds is significantly lower than that in cells of male birds. (J3.135.w4)

Microsatellite DNA probes

  • Microsatellite probes have been found which allowed sex determination of several bird species, but were not useful for other species. Testing of other probes could be beneficial to provide a more universal approach to bird sexing by this method. (J50.110.w1)
Surgical (laparoscopic) sexing
  • This is a definitive method of sexing. (B13.29.w8)
  • This is very reliable if carried out by an experienced person. (B13.29.w8)
  • It can be difficult to distinguish between the male and female gonads in some immature birds. (J3.112.w3, J23.18.w6)
    • If there is doubt, an attempt should be made to locate the second gonad. If this is present then the bird is male. (J23.18.w6)
    • Location and identification of the gonad is facilitated in some species by pigmentation of the gonad. (J5.31.w7)
    • Sexing is particularly easy in matre females, in which the ovary with developing follicles is easily distinguished. (J5.31.w7)
  • Errors can occur if this procedure is used on immature birds in which the gonads have not yet differentiated. (B13.29.w8, J5.31.w7)
  • Errors can occur if this procedure is carried out by inexperienced personnel. (J23.16.w7)
  • Alimentary tract distention can make examination of the gonads difficult. (J3.112.w3)
  • Excessive fat deposits around the kidneys and gonads can prevent viewing of the gonads. (J3.112.w3, J23.18.w6)
    • A 1 mm diameter probe inserted alongside the laparoscope can be used to tease the fat away from the gonad for observation. (J23.18.w6)
  • This is an invasive procedure and requires a general anaesthetic. (B13.29.w8, J5.31.w7)
  • There is an increased risk of injury to the bird if this procedure is carried out be inexperienced personnel. (J23.16.w7)
  • This procedure can be carried out under manual restraint with local anaesthetic injected at the laparoscopic site, or under general anaesthetic. (J23.18.w6)
    • There is an increased risk of physical injury to the bird if the procedure is carried out under manual restraint. (J3.112.w3)
    • There is a small risk associated with general anaesthetic and this risk is increased if the bird is not healthy at the time of the examination. (J3.112.w3, J3.112.w4, J3.112.w5)
  • When conducting the laparoscopic examination, abdominal structures are visualised and this may allow detection of disease or dysfunction of the gonads or other organs. (B13.29.w8)
Ultrasonographic sexing
  • Ultrasonography has been used to sex birds of prey. This used a probe placed into the cloaca and detects the presence or absence of an oviduct (detecting the vaginal portion of the left oviduct). The vaginal segment of the oviduct was visualised as "an elongated hypoechoic structure with sharply demarcated echogenic borders" within which "the vaginal lumen was inconsistently detected as a thinner linear echogenic structure." (J2.26.w5)
Waterfowl Consideration
  • Many ducks can be sexed on the basis of plumage characteristics. This is not possible for swans, true geese, sheldgeese, whistling-ducks.
  • Vent-sexing is commonly used to distinguish adult waterfowl of monomorphic species and is also used to determine the sex of downy young. See Vent Sexing of Waterfowl
Crane Consideration Correct sexing is essential if cranes are to be bred. Cranes are monomorphic
  • Ideally, the sex of cranes should be confirmed when they are chicks, allowing same-sex grouping during socialisation to avoid the risk of cranes which have been reared together considering each other as siblings and therefore not forming a true pair if placed together as adults. (B115.6.w8, P76.1990.w2)
Correct sexing of cranes is extremely important for breeding programmes. 
  • It is important to correctly determine the sex of cranes before pairing.
  • Sexing may be carried out using a variety of methods including morphometrics, behavioural observation, particularly during the Unison-call, vent sexing, faecal steroid analysis, genetic sexing and surgical sexing (laparoscopy). (B105.13.w4, B115.11C.w12, J23.14.w5, P89.1.w1)
Visual - colour
  • Cranes are generally visually monomorphic; males and females cannot be distinguished visually. (B115.11C.w12, J346.92.w1)
Morphometrics - size
  • In most species of cranes, males are larger than females, although there is an overlap. (B115.11C.w12, J23.14.w5, P89.1.w1)
  • Larger-than-average males and smaller-than-average females can be sexed based on size. (B115.11C.w12)
  • For captive cranes of six species, males on average were 14.5-28.5% heavier than females, with 2.5-11.7% longer culmens and 3.3-11.1% longer tarsi than conspecific females. (B115.11C.w12)
  • Weights are less useful for sexing than are linear measurements, because they show considerable seasonal variation, particularly in temperate and arctic-nesting species, as well as differences between wild and captive birds and between captive birds kept at different locations. (B115.11C.w12, P87.6.w2)
  • In general, wing chord and tail measurements are not useful for sexing cranes due to variations caused by feather wear, particularly in captive cranes. (B115.11C.w12, P87.6.w2)
  • In wild Grus grus - Common crane, males and females can be distinguished by measurement of five paramenters: the head height, wing length, tarsus length, length of the third finger and tail length. (B115.11C.w12, ****Markin)
  • In captive Grus japonensis - Red-crowned crane, a discriminant function using measurements of the tail, wing chord, tarsus and culmen has been developed for sexing. (B115.11C.w12)
  • Discriminant functions have been developed also for sexing Grus virgo - Demoiselle crane, Grus leucogeranus - Siberian crane, Grus canadensis - Sandhill crane, Grus vipio - White-naped crane. (B115.11C.w12)
  • In any given pair of wild Grus rubicunda - Brolga, the male is larger than the female. (J440.28.w1, B115.11C.w12)
    • While males were larger on average than females in all measurements (weight, length of body, wing, culmen, tarsus, middle toe), there was considerable overlap. (J440.28.w1)
Voice, Display and Behaviour

General behaviour

  • In wild crane pairs, nearly always the male leads and the female follows. The main is the main defender, spends more time watching for intruders, and generally adapts more erect and aggressive postures, holding his head higher; females are more likely to develop a neck-retracted submissive posture on the approach of an intruder. However, in captive pairs, the female often, perhaps usually, initiates dancing and calling. (B115.11C.w12)
  • Hand-reared males tend to be very aggressive, often attacking people, particularly once paired, while hand-reared females approach people but usually are submissive rather than aggressive, although she may become more aggressive once paired. In general, the male displays more intensely than the female, and approaches an intruder more closely. (B115.11C.w12)
  • Males generally expand their crowns (Bare-skin expansion) or wattles (Wattle-expansion) more than do females; during conflicts, the wattles of a male Grus carunculatus - Wattled crane may be larger than those of the female. (B115.11C.w12)
  • Experienced keepers with several immature birds often can make an "intelligent guess" about the sex of each bird, based on relative size and behaviour; however, these guesses can be wrong. (N28.10.w1)

Guard-calls

  • In all the Grus spp. (although not in the Balearica spp.), males of a given species produce their calls at a lower pitch than do females. The difference is most obvious when hearing both a male and a female calling. Experienced personnel can distinguish whether an individual calling crane is male or female. (B115.11C.w12)
  • Balearica regulorum - Grey crowned-crane uses ka-wonks only in their guard-call; the female's ka-wonk averages slightly longer than that of the male. (B115.11C.w12)

Unison calls

Visual and vocal characteristics during displays can be used to determine sex in most crane species. (B115.11C.w12, J23.14.w5, J54.2.w1, P89.1.w1, P1.1980.w8, Th11)

  • In Balearica spp., differences between males and females are minor and are insufficient to allow sexing by ear. (B115.11C.w12) 
  • Grus virgo - Demoiselle crane. The female starts the Unison-call, throwing her head back beyond the vertical; she then either holds her head position during the Unison-call or gradually returns to a more horizontal position. The male follows her first note and gives lower-pitched, longer, more broken notes, with his neck vertical and his bill held at 45 degrees above the horizontal. One female call is given per male call. (B115.11C.w12)
  • Grus paradisea - Blue crane. The female normally throws her head back to 20 degrees beyond vertical, while the male throws his head and neck back to about 40 degrees beyond vertical, and raises his humeri above his back. One female call is given per male call. (B115.11C.w12)
  • Grus carunculatus - Wattled crane The female starts the Unison-call by quickly lowering her head to shoulder level then raising her neck quickly so that her head is raised to about 30 degrees in front of vertical, and holds it there. The male similarly lowers his head then thrusts it up, neck upright and bill 70 degrees above the horizontal. The male's call starts after that of the female; the first note is long and partly broken, then he gives longer, fewer, lower-pitched notes, ending with a longer, broken note during which he raises his humeri 20 degrees above his back. 
  • Grus leucogeranus - Siberian crane The female's voice is higher-pitched than the male's, but it may be necessary to hear both to distinguish this, as some males have a relatively high pitched voice. The female gives one call for each call of the male. Either bird may start the call; when the male starts it he swings his head up rapidly then throws it down near his chest, giving a long preliminary note. Either bird may walk during the Unison-call and either bird may lower its primaries.
  • Grus canadensis - Sandhill crane usually the female starts the Unison-call, giving an explosion of rapid notes; sometimes the call is started by the male. The female gives two or three notes for each note from the male. Both birds hold their neck upright, but the female holds her bill nearly horizontal, flicking it up at each note, while the male holds his head further back and his bill more vertical. The female has a higher-pitched voice than the male. 
  • Grus rubicunda - Brolga The Unison-call is usually started by the female; she gives perhaps two notes for each note given by the male (1.4 ,Th11) and has a higher-pitched voice. The female holds her neck vertical and bill slightly above the horizontal, while the male extends his neck back beyond the vertical; the male raises his humeri high above his back and completely lowers his primaries, while the female does not move her wings. 
  • Grus antigone - Sarus crane The Unison-call is usually started by the female; she gives two or three notes for each note given by the male, and has a higher-pitched voice. The female holds her neck vertical and bill slightly above the horizontal, while the male extends his neck back beyond the vertical; the male raises his humeri high above his back and completely lowers his primaries, while the female does not move her wings.
  • Grus vipio - White-naped crane The Unison-call is always started by the female; she gives two notes for each note given by the male, and has a higher-pitched voice. The female holds her neck vertical and bill slightly above the horizontal, while the male extends his neck back beyond the vertical; the male raises his humeri high above his back and completely lowers his primaries, raising and lowering his elbows with each call, while the female does not move her wings.
  • Grus grus - Common crane The female's voice is higher pitched than the male's and she gives typically three calls for each call of the male. During the call the male typically extends his head far back over his body, bill upright, and raises his humeri, often raising and lowering these with each note. The female maintains a more vertical stance and only rarely raises her humeri during the Unison-call. 
  • Grus monacha - Hooded crane The female's voice is higher pitched than the male's and she typically gives two calls for each call given by the male. The female typically holds her neck vertical or slightly forward of vertical. The male typically extends his head back over his body and he usually raises his humeri during the display; often he may raise and lower the humeri with each note. 
  • Grus americana - Whooping crane The female's voice is higher pitched than the male's and she typically gives two calls for each call of the male. Both birds have their bill raised to perhaps 20 degrees from the vertical. During the call the male extends his head far back over his body, and raises his humeri, often raising and lowering these with each note. The female typically holds her neck vertical or slightly forward of vertical; she occasionally raises her humeri during the Unison-call. 
  • Grus nigricollis - Black-necked crane The female's voice is higher pitched than the male's and she typically gives two or three calls for each call of the male. The female typically holds her neck vertical or slightly forward of vertical. The male typically extends his head back over his body and he usually raises his humeri during the display; often he may raise and lower the humeri with each note. 
  • Grus japonensis - Red-crowned crane The female's voice is higher pitched than the male's and she typically gives two or three calls for each call of the male. The female typically holds her neck vertical or slightly forward of vertical. The male typically extends his head back over his body and he usually raises his humeri during the display; often he may raise and lower the humeri with each note. 

(B115.11C.w12, Th11)

Vent sexing
  • This can be used by experienced personnel for sexing most adult and some subadult and yearling cranes. (B115.11C.w12, J54.2.w1)
  • The bird is caught and massaged as for artificial insemination (see: Artificial Insemination in Cranes), while a second person examines the cloaca. (B115.11C.w12)
    • In male cranes, in the middle of the unmanipulated cloaca, two small, raised papillae can be seen next to each other, each about 1 mm in diameter, usually lighter in colour than the surrounding tissue. In a crane of more than one year of age, if these are present the crane is male; if absent, the cranes is female. (B115.11C.w12, J23.14.w5)
      • In brolgas, the papillae were slightly ventral on either side of the cloaca. (J440.28.w1)
    • In female cranes more than a year old, the opening to the oviduct may be visible (lower left of the cloaca) and the bursa of Fabricius may be visible as a small spot near the top of the cloaca. These are most visible in reproductive females during the breeding season. (B115.11C.w12, J23.14.w5, J440.28.w1)
      • Additionally, the pubic bones are further apart in breeding females than in males - from being seprated by approximately the width of a man's finger, as in males, the distance increases to about four times that distance at the time eggs are laid. (J23.14.w5)
Faecal steroid sexing
  • Faecal steroid sexing, based on the oestrogen/testosterone ration (higher in females) and a low absolute testosterone level, can be used in cranes. (B115.11C.w12)
    • Ratios may overlap occasionally due to seasonal and age variation, particularly outside the breeding season. (B115.11C.w12)
    • The best results are obtained from adult cranes during the breeding season. (B115.11C.w12)
    • This method also can be used to determine the sex of chicks, by testing the waste material left in the shell at hatching (egg wastes sample a relatively long time period and sex hormones are important in the sexual differentiation of the embryo). (B115.11C.w12)
Genetic sexing
  • This involves the use of a blood sample or feather to provide genetic material for testing. Methods using a feather are preferable as feather collection, storage and transport can be carried out easily, quickly and cheaply. (J346.92.w1)
  • It is advisable to contact the company which will perform the sexing in advance, to check the sample required (blood or feather pulp), sampling instructions, postage instructions and to obtain any required shipping media etc. (B115.11C.w12)
Karyotyping
  • Karyotyping or chromosomal sexing can be used to determine the sex of cranes of any age. (JB115.11C.w12, J23.14.w5, P1.1980.w8, P89.1.w1, P90.1.w3)
  • In birds, males have two Z chromosomes (ZZ) while females have a Z and a W (ZW). (P90.1.w3)
  • In a chromosome spread (from dividing mitotic cells in metaphase), female cranes have four or five (depending on the species) macrochromosomes and one unpaired, because the Z chromosome is about the same size as the fourth or fifth macrochromosome, while the W chromosome is much smaller. In males, which are ZZ, the macrochromosomes will all be paired. (B115.11C.w12)
  • Karyotyping can be carried out on cultured blood cells or feather pulp from a growing feather. (B115.11C.w12, J23.14.w5, P90.1.w3) 
    • In cranes, good chromosome spreads are more often created from feather pulp culture than from blood. (B115.11C.w12)
  • An appropriate laboratory should be identified and contacted in advance before any samples are collected. (B115.11C.w12)
  • Feather pulp: 
    • A large growing (emerging) feather is pulled, the shaft is wiped with alcohol, the basal 2-3 cm is cut off the feather with sharp scissors and placed into media supplied by the commercial laboratory. (B115.11C.w12)
    • If no large growing feathers are available, pull two feathers and wait three to four weeks for a new feather to start to grow. Tail feathers or tertials should be pulled, rather than primary wing feathers, to reduce the risk of malformed primaries developing. Two feathers are pulled initially in case one does not re-grow immediately. To pull a feather, use a large pair of haemostats or pliers, grasp the feather as close to the base as possible, and pull it straight out. When pulling a growing feather it is important to pull the whole feather; if the feather breaks, leaving part of the shaft in the follicle, bleeding can be prolonged and even on rare occasions fatal. (B115.11C.w12)
      • In the USA, Avian Genetics Sexing Lab and Avigen offer commercial feather pulp sexing.
  • Blood culture:
    • Five hours before blood is to be taken, remove the crane's food. Prepare a sterile 3 mL syringe: place 0.2 m: sodium heparin (10,000 units/mL) into the syringe and work the plunger to ensure the inside of the barrel of the syringe is coated. Draw 2-3 mL blood from the crane's jugular or brachial vein into the syringe. Invert the syringe several times to ensure adequate mixing of the anticoagulant with the blood. Keep the blood refrigerated. Send the blood to an appropriate laboratory as soon as possible. (B115.11C.w12)
    • In North America, some major university research laboratories carry out karyotyping from blood culture. (B115.11C.w12)
DNA Probe
  • A DNA probe technique using restriction fragment length polymorphism (RFLP) is available commercially (Zoogen, Inc. in the USA). (B115.11C.w12)
    • This technique uses the difference in the lengths of the non-coding DNA of the CHD-gene from the W and Z chromosomes. (W659.Feb07.w1)
    • A 0.02 mL blood sample mixed with ethanol is sent to the sexing company. (B115.11C.w12)
  • Blood (0.01-0.05 mL) can be taken from the chorio-allantoic vessels under the shell membrane at 16-25 days of incubation for sexing of embryos (by DNA probe analysis) prior to hatching. (P1.1997.w10, P4.1998.w2)
    • There is a risk of the embryo not surviving through to hatching; this risk decreases with increasing experience of the person carrying out the procedure. (P1.1997.w10, P4.1998.w2)
    • This technique may be more successful on eggs which are relatively thin shelled and lightly pigmented, making it easier to identify the chorio-allantoic vessels by candling. (P1.1997.w10, P4.1998.w2)
    • The technique may be more successful if blood is collected during the second half of incubation. (P1.1997.w10, P4.1998.w2)
    • Careful management of the egg is important following the procedure, during incubation and particularly during hatching. (P1.1997.w10, P4.1998.w2)
  • A female-specific DNA fragment (CSL-W) has been isolated and cloned by PCR from female whooping cranes. This successfully confirmed sex of 100% of 18 tested cranes. It has been used with plucked body (contour) feathers (fully developed or moulted feathers); in combination with a rapid DNA extraction method it can give a result in less than 10 hours. Using a different DNA extraction method it could be used on blood samples. (J346.92.w1)
Genome Size
  • This method is rarely used, but can be carried out on very small blood samples from cranes. (B115.11C.w12)
Surgical (laparoscopic) sexing
Sexing can be carried out by laparoscopic examination of the gonads (generally when the birds are six months old or older). (J54.2.w1, N28.10.w1, P1.1980.w8)
  • Surgical sexing may be carried out via laparoscopy or an otoscope. (B105.13.w4, B115.11C.w12, P89.1.w1)
  • The crane should be anaesthetised to reduce stress and the risk of injury. (B115.8.w4, B115.11C.w12)
  • Males have paired, white to tan testes. In immature males they are small (0.5-1.21 x 0.1-0.2 mm) and are usually avascular. In mature the testes are much larger (3-5 x 2-3 cm) and the surface is vascularised. (B115.11C.w12)
  • Females have a single (left) ovary. In very young females it may nt be visible; if it is, it is pink to tan, flat and looks like "pebbled" fat. In subadult females the surface appears granualr and in mature females the follicles give a "cluster of grapes" appearance. B115.11C.w12
Associated Associated techniques linked from Wildpro

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Pair / Group Formation

  • Captive animals frequently are not allowed to chose their own mates. Rather, the choice is made for them on the basis of genetics or expediency (available individuals). However, in a number of species, such as cranes (Gruidae), it is recognised that mate choice plays an important role in pairing, and that some pairings, chosen by humans, will never form proper pairs leading to the production of eggs and offspring. Similarly pink pigeons, Columba mayeri have been paired on the basis of genetics but shown no interest in one another (B105.15.w2).
  • In establishing pair bonds between monogamous birds, whether the pair will be of seasonal or life-long duration, courtship behaviour is essential. Depending on the species, restricted horizontal or vertical space, pinioning etc. may interfere with normal courtship displays. 
  • In general, newly-introduced birds are either indifferent or intolerant to one another, with the indifference or intolerance decreasing as the pair bond strengthens. In a variety of species it has been shown that stronger pair bonds may be formed if subadult birds are placed as flocks in large enclosures and allowed to choose their own mates. However genetic, demographic and other considerations may make this impossible.
  • Forced pairings may result in problems of incompatibility and/ aggression. Initial introductions may be carried out by placing an intended pair of birds in visual but not physical contact with one another - on opposite sides of a fence or in adjacent cages. Signs of pairing including cessation of threat displays directed towards one another, the development of synchronous behaviour (feeding at the same time, etc.), deliberate and regular maintenance of close proximity to one another and exhibition of specific courtship behaviours are signs which indicate the birds might be placed together.
  • Age and previous breeding experience may also be factors affecting mating, for example with pairs of birds frequently being of similar age to one another.
  • Unpaired birds may interfere with pairs and disrupt breeding.

(B96, B105.15.w2, B115, V.w5).

Waterfowl Consideration
  • Most waterfowl form monogamous pairs, either lifelong, as in the swans and geese, or seasonal. In some species, courtship behaviour is seen in groups and breeding may be increased if these waterfowl are maintained in appropriate groups during the courting season.
  • In waterfowl which form long-lasting pair bonds, such as swans, it is generally recommended that some consideration be given to the relative ages of the two birds. Pairing an adult male with a very young female may cause problems, with the female reacting with fear to aggressive displays by the male.
  • Allowance should be made for the age at which birds of each species reach sexual maturity.
  • Great care should be taken in forming pairs in species where aggression between males and females is known to occur commonly.
  • Plumage colouration may be associated with mate choice in lesser snow geese Anser caerulescens caerulescens (Anser caerulescens - Snow goose) and Branta bernicla - Brent goose.
  • N.B. Waterfowl are known to be susceptible to imprinting on the wrong species if foster-reared or artificially reared. This may lead to individuals which appear incapable of forming a normal pair-bond with a member of their own species.

(J8.17.w1, B7, B11.33.w1, B13.46.w1, B105.15.w2, B106).

Crane Consideration

Sandhill cranes in divided pen. Click here for full-page view with caption.

  • Cranes will not always accept the mate chosen for them. (B105.13.w4, N1.80.w1)
    • If two cranes have been kept together for two years or longer, but shown no signs of courtship, it may be better to split the birds and try to pair them with other individuals. (N1.80.w1, V.w5)
  • In whooping cranes, successful reproduction requires the male to be dominant over the female. (B105.15.w2)
  • Cranes normally form a pair. Occasionally, it is possible to match a male with two females, each in a separate pen, and have all three birds unison-calling and both females laying eggs. (P91.1.w6)
Signs of pairing
  • The strength of the pair bond is generally assessed by observing the presence or absence of a variety of behaviours within the putative pair, including proximity, behavioural synchronisation, dancing, territorial defence, and calling. Copulation and egg-laying are ultimate indicators of a strong pair bond. (N1.103.w1, P76.1990.w2)

Synchronised activities and proximity

  • As cranes start to pair, the two birds spend more time in close proximity to one another, and start to synchronise their maintenance activities: feeding, resting and preening at the same time as one another. (P76.1990.w2)
  • Strong pairs spend much of their time in close proximity to each other. (N1.103.w1)
  • Pairs which are firmly established act together and may show highly synchronised behaviours such as threat walking and grass pulling. (P76.1990.w2)
  • In the wild, close proximity of pairs reduces the chance of a crane appearing to be alone - which may encourage another crane to approach to try to form a pair. (N1.103.w1)
  • At ICF, paired cranes have a mean distance apart of about 2 m (6ft 7 inches), and are usually 1-1.5 m (1ft 3 ins - 4ft 11 ins) apart during territory defence, roosting, loafing, preeding, foraging and dancing. (N1.103.w1)

Territorial vigilance and aggression

  • Paired cranes show increased aggression to other cranes and to humans. The male of an established pair will defend the female; the female may assist the male in defence or may stand back. (P76.1990.w2)
  • The most successful pairs at ICF, which lay eggs consistently, show strong territorial defence - charging into pen fences, following aviculturists as they walk along the perimeter of the pen, attacking aviculturists. (N1.103.w1)

Dancing

  • Dancing can be associated with mating, but also has other functions. (N1.103.w1, P95.1.w1)
    • Dancing is a series of threat behaviours which may express nervous tension or elation. (N1.103.w1)
  • Dancing is not necessarily a sign of pairing; it is often seen in unpaired birds and even in chicks. Dancing sometimes is perceived as aggression and can precede other threat displays. (P76.1990.w2)
  • Strong pairs will often dance, both birds participating freely, neither intimidating the other. This is seen particularly after sunrise and in the evening. Pairs while seldom dance may not have a strong pair bond. (N1.103.w1)
  • However, frequent dancing does not necessarily indicate that the pair will be reproductively successful. (N1.103.w1)
Unison calls, guard calls and contact calls
  • The two birds start to guard call together as the bond develops, and also start exchanging contact calls to help keep track of each other's location. (P76.1990.w2)
    • Contact calls act as a feedback mechanism, each bird informing the other of its immediate proximity. They may be exchanged e.g. while foraging, also if there is a disturbance which both cranes are focusing on. (N1.103.w1)
  • Unison calls, usually initiated by the female, are exchanged as the bond strengthens. (P76.1990.w2)
    • The unison call has both sexual and threat functions. (P76.1990.w2)
    • The unison call is a territorial proclamation; it also serves to reinforce the pair bond strength following copulation. (N1.103.w1)
    • In general, the presence of the unison-call is a sure sign of a strong pair bond. (N1.103.w1)
    • Note: If a pair are in the same pen, they will unison call together directing this at intruders. If in a subdivided pen, they may direct the unison call at one another; this can be an artifact caused by the separation. However, sometimes the female is calling sexually but the male is calling aggressively; in such cases if they are placed together the male is likely to attack the female, but if kept separated by a fence, the female may lay eggs. (P76.1990.w2)

Location calls - testing the pair bond

  • One way in which pair bond strength can be measured is with the "location call test". This involves moving one bird of a putative pair to another enclosure - not directly adjacent, but within auditory range. (N1.103.w1)
    • Potential stressors such as visual contact with other cranes should be avoided during the test. 
    • After the birds have had several minutes to calm down, if the birds are well paired they should start location calling. the location call is a single note call similar to the guard call, but often slightly longer and more drawn out. 
    • If neither bird gives any location calls, they probably do not have a strong pair bond.
    • If one bird only is calling, this may indicate that while this bird is attracted, the other is not. 
    • Visually, strongly paired birds undergoing this test are likely to be frantically pacing the enclosures, trying to get back to the other bird.

    (N1.103.w1)

Copulation and egg laying

  • The cumulation of pairing behaviour is copulatory behaviour and egg laying. (P76.1990.w2)

Pair formation in flocks

  • If young cranes of a given species are allowed to form a juvenile flock, they may develop liaisons and start to initiate pairs; formation of pairs usually peaks at two to three years of age. (P76.1990.w2, N18.45.w1)
    • A set of food and water stations must be provided for each potential pair, allowing the pairs to develop territorial behaviour, facilitating pair formation, while ensuring that subordinate birds can still access food and water. (P76.1990.w2)
    • One two cranes show signs of forming a pair, they should be removed from the juvenile flock and placed in an individual breeding pen. (P76.1990.w2)
    • It is important to remove strong pairs quickly in order to reduce the stress on subordinate birds in the flock. (P76.1990.w2)
    • Development of a pair bond may be inhibited by the presence of more dominant birds and the inability to secure an isolated territory; compatible cranes which form liaisons with birds of the opposite sex therefore should be placed into an individual enclosure to facilitate formation of the pair bond. (P76.1990.w2)
    • Separation of pairs at two years old is optimal. (P76.1990.w2)
    • When pairs are allowed to form in this manner, the pairs formed first tend to be strongest. Submissive birds paired in flocks in this manner tend not to breed properly. (P76.1990.w2)
    • Note: 25% of pairs formed in the flock situation have gone on to lay eggs; in comparison, 71% of those introduced by socialisation of unfamiliar birds have produced eggs. (P76.1990.w2)
    • In a group of five male and three female Balearica regulorum - Grey crowned-crane, signs of pair formation were seen within hours of the birds being put together and there were clear signs of pair-bonding behaviours by the second day for two sets of birds. The remaining three males and one female did not show any signs of pair formation even after they were separated from the first two pairs. (N18.45.w1)

Pair formation by socialisation of unfamiliar birds

  • Place a male and a female crane in adjacent halves of a subdivided pen.
  • Observe the birds; if excessive aggressive behaviour is seen, it may be necessary to temporarily provide a partial visual barrier, such as tennis windscreen netting, placed on the aggressor's side of the fence.
    • This also reduces the risk of injury.
    • Once the cranes have adjusted to being adjacent, the visual barrier can be removed gradually, initially in areas with low activity of the cranes and gradually proceeding to areas where they have more contact.
  • Continue observing for signs the cranes are compatible. 
    • Cranes which do not show aggressive behaviour to one another may be introduced under supervision; if they continue not to show aggression, they may be left together to allow a pair bond to develop gradually. (P76.1990.w2)
    • More usually, cranes are maintained in the adjacent pens until they show clear signs of pairing behaviour such as proximity, synchronised maintenance activities, guard calls together and unison calls. (P76.1990.w2)
      • Socialisation may be best carried out in summer or autumn (fall), when aggression levels are reduced, rather than earlier in the year when they are seually active and aggression levels tend to be higher. (P76.1990.w2)
      • The more dominant crane (usually the male) is introduced into the less dominant bird's pen, then the birds are watched constantly for signs of aggression. (P76.1990.w2)
      • If the birds show strong aggressive behaviour, they are separated immediately before strong fear patterns are established. (P76.1990.w2)
      • Minor aggressive behaviours, such as light pecks or stand-offs are watched closely in case stronger aggression develops; some testing between the birds is required to establish their relationship. (P76.1990.w2)
      • After a few minutes to several hours of supervised interaction (depending on the birds' behaviour and staff availability), the birds are separated back into their own pens. (P76.1990.w2)
      • After several days of successful socialisation, the birds are left together unsupervised, initially for a short period, then for longer periods, but are still separated at night. Only after they have been left together safely for several full days are they left together permanently (day and night). (P76.1990.w2)
    • If the pair show normal pair behaviours, and the female lays eggs, but the male is highly aggressive, it may be necessary to keep the pair permanently separated from one another by a fence and use artificial insemination to fertilise the eggs. (P76.1990.w2)
    • Note: killing of females by their mate after several years of successful cohabitation can occur. It is thought this is due to external stimuli such as new neighbours resulting in increased levels of aggression in the male and this aggression then being redirected at the female. (P76.1990.w2)

Factors affecting pairing

  • Mate choice may be affected by early experience. (P76.1990.w2)
    • Hand-reared cranes commonly imprint on humans. (P76.1990.w2)
    • Parent-reared chicks are strongly imprinted on the correct species and have the greatest opportunity for correct learned behaviour. (P76.1990.w2)
  • Development of a strong pair bond generally requires a balance in dominance, with the male dominant, but the female not too submissive to the male.
    • If the female is dominant, generally a strong, stable pair does not form and the female does not lay eggs. (P76.1990.w2)
    • If the female is too submissive, there is a higher chance of aggression from the male onto the female. (P76.1990.w2)
    • Methods of increasing male dominance (e.g. if introducing a young male to an older, dominant female) include building a mound on the male's side of the pen to make him relatively taller, and brailing one wing of the female for the initial encounter. (P76.1990.w2)
  • Rapid pairing can occur, for example:
    • mature, dominant birds which have recently lost their mates and are ready to re-pair;
    • dominant two-year-old cranes entering their first breeding season and with balanced reproductive drives.

    (P76.1990.w2)

  • Forming a pair between an experienced crane and a novice may be advantageous in that the inexperienced bird can learn appropriate behaviour from the experienced crane, but imbalances in dominance and sexual drive may make it harder for such pairs to become established. (P76.1990.w2)
  • It may be advantageous to pair a wild-caught female with a captive-reared male, whose confidence can reduce the stress on the female, while the interaction with the wild-caught female may stimulate the expression of normal behaviour in the captive-reared bird. (P76.1990.w2)

Techniques to stimulate and strengthen pair bonds

  • Allowing a pair to hatch and rear a chick may improve the pair bond. (B115.6.w9)
Associated techniques linked from Wildpro

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Hybridisation

Hybridisation is a common problem in captive animals, due to closely-related species, or subspecies, normally separated (e.g. geographically) being brought together. In most cases, hybrids are infertile, although hybrids between subspecies or between closely related species may be fertile. Hybridisation is sometimes a useful tool in indicating ancestral relationships, but should usually be avoided. Fertile hybrids may be a threat to the maintenance of the pure form of either or both parent species or subspecies.
Waterfowl Consideration
  • Hybridisation is likely to occur if closely-related waterfowl species are kept together. Hybridisation reduced by not mixing closely related species or subspecies, e.g. the mallard (Anas platyrhynchos - Mallard)and its close relatives, silver teal (Anas versicolor - Silver teal) and puna teal (Anas puna - Puna teal)(formerly Anas versicolor versicolor and Anas versicolor puna, respectively), Chilean teal and sharp-winged teal (subspecies of Anas flavirostris - Speckled teal), European wigeon (Anas penelope - Eurasian wigeon) and American Wigeon (Anas americana - American wigeon), blue-winged and cinnamon teal (Anas discors - Blue-winged teal and Anas cyanoptera - Cinnamon teal), red-crested and rosy-billed pochards (Netta rufina - Red-crested pochard and Netta peposaca - Rosy-billed pochard). Geese also tend to hybridise, particularly emperors (Anser canagica - Emperor goose) and Lesser whitefronts (Anser erythropus - Lesser white-fronted goose).
  • The tendency to hybridise is decreased if pairs are given time to become established as a mated pair before being introduced into a mixed-species group. Odd geese (unpaired) may hybridise particularly if reared with another species.
  • Certain individual birds have a tendency to choose mates of different (sometimes very different) species and need to be kept apart. The tendency towards interbreeding occurs more commonly in birds which have been reared in a mixed-species group; species should be kept separate during the rearing period if possible, for this reason.
  • Hybridisation also occurs in the wild, particularly where humans have introduces a species into an area already occupied by a closely related species. Crosses in the wild between native species and introduced Anas platyrhynchos - Mallard are of concern, for example in New Zealand, where they hybridise with Anas superciliosa - Pacific black duck; mallard also hybridise with Anas rubripes - American black duck in North America. Similarly, the North American species Oxyura jamaicensis - Ruddy duck is causing concern in Europe; individuals bred in collections in the UK have become feral and the growing population is threatening the closely-related Oxyura leucocephala - White-headed duck in Spain.

(J23.13.w7, B7, B29, B37.x.w1, B97, V.w5).

Crane Consideration
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Failure to Produce Eggs

A variety of external factors interact with endogenous hormonal rhythms to stimulate or suppress egg production in birds. These may include daylength, temperature, presence of a mate, rainfall or humidity, nutrition/food supply, chick rearing, competition (seen as squabbling or harassment), predator pressure, inclement weather and other causes of stress.
  • Environment: lack of specific environmental cues (daylength, rainfall), lack of suitable nest sites.
  • Nutritional factors: Deficiencies in general nutrition or in essential micronutrients may lead to failure to produce eggs.
  • Age: Depending on species, females may be sufficiently developed to lay eggs by one year old or less, or not until they are several years old. In old age the left ovary (the only active ovary in most bird species) may become inactive.
  • Pairing: When there is a persistent failure to lay eggs the possibility that both birds of a "pair" are male must be considered. Depending on species, the formation of a proper pair bond may be essential for egg laying to occur. If a female is imprinted on the wrong species she may fail to lay eggs unless a mate of her preferred species is provided.
  • Stress: Constant harassment and squabbling, also other causes of stress, including disturbance by humans, may reduce or prevent egg laying.

(B95, B105.14.w1, B105.15.w2, B106)

Waterfowl Consideration
  • If a "pair" of waterfowl consistently fail to lay eggs, the possibility that a mistake has been made in sexing the birds, with both birds being male, should be considered. This is most likely to occur in monomorphic species.
  • If eggs are always removed for artificial incubation and the waterfowl never allowed to rear any downies, they may stop laying.
  • The Nene (Branta sandvicensis - Nene) is known to respond to a small increase in photoperiod.

(B105.14.w1, N1.101.w1)

Crane Consideration
  • Failure to lay eggs may occur because both cranes in a "pair" are male. It is important to determine the gender of cranes before forming a pair. see above: Determining Sex 

Age and pair bonds

  • In general, female cranes will lay eggs only if they are paired. (B115.3.w2, P76.1990.w2)
    • Cranes reared in isolation from their own species may become incorrectly sexually imprinted - for example onto humans. (J23.17.w5)
      • Incorrect sexual imprining can be prevented by allowing hand-reared chicks to see other chicks of the same species, or older conspecifics, in adjacent pens. (J23.17.w5)
    • A human-imprinted Grus americana - Whooping crane was induced to lay when a human male took on the role of mate, established a pair bond with her, spent much time with her, danced with her morning and evening, helped nest building and territory defence etc. (N27.8.w1)
  • Cranes usually start to produce eggs one to two years after a pair bond is formed. (B115.3.w2)
  • Laying has been recorded in cranes which are just two years old. This has been seen in captive Grus carunculatus - Wattled crane, Grus japonensis - Red-crowned crane, Grus antigone - Sarus crane and Grus canadensis - Sandhill crane; laying at two years old occurs in about 25% of Mississippi sandhill cranes. (B115.3.w2)
  • Improved species-specific husbandry may lead to earlier breeding in species which previously have bred later in captivity than in the wild. (B115.3.w2)
  • Allowing pairs to incubate, hatch and rear a chick may improve pair bonding, egg laying and fertilisation. In pairs which appear to be compatible but are not breeding, adoption of a chick may lead to changes in behaviour and improved breeding. (N1.80.w2, P92.1.w6)

Environmental cues

  • Most cranes normally nest near or surrounded by water. Cranes kept in enclosures which include a marsh area, flowing stream or pools may be stimulated to breed, and these conditions should be provided where possible, although this must be balanced with potential disease problems associated with standing water. (B115.3.w2)
  • For cranes which in the wild breed at high latitudes, provision of an extended photoperiod by use of artificial light may be needed to stimulate reproduction when they are kept at lower latitudes. (B115.12.w8, P92.1.w6) This has been used for breeding Grus leucogeranus - Siberian crane, Grus monacha - Hooded crane , greater sandhill cranes Grus canadensis tabida  (Grus canadensis - Sandhill crane) and Grus americana - Whooping crane (B105.13.w4, J54.2.w1, N27.8.w3, P76.1990.w2, P92.1.w6)
    • At Patuxent Wildlife Research Center, additional lighting is provided for Grus americana - Whooping crane starting in February, six to eight weeks before the expected onset of laying, and increased gradually so that by the day length will equal that which would be occurring at Wood Buffalo National Park (the natural breeding grounds) at the same time that the Patuxent temperatures are similar to those of Wood Buffalo at the start of the breeding season. (J54.2.w1)
    • At ICF, additional lighting is provided for Grus leucogeranus - Siberian crane, starting at 16 hours and increasing to give 23 hours "daylight" per day. (P96.1.w1)
    • Provision of an extended photoperiod may also be useful for cranes which breed at mid-latitudes. (B115.3.w2)
  • An overhead sprinkler, controlled by timers, can be used to simulate the rainy season and encourage breeding in Grus rubicunda - Brolga and in Balearica spp.. (B115.12.w8, P96.1.w1, P92.1.w6)
  • Temperature cues may have an effect: the onset of hot weather in summer may terminate semen production in some species such as Grus leucogeranus - Siberian crane. (B115.3.w2)

Disturbance and egg searches

  • Cranes may fail to lay if they are disturbed or feel insufficiently secure in their territory. (B115.3.w2)
    • Cranes may fail to lay if they are disturbed for example by being moved between pens or by construction activity near their pen during or just prior to the breeding season. (P87.7.w5)
    • Cranes may fail to lay if they do not feel they have a secure part of their enclosure; this is most likely to occur with birds on public display. If this is or might be a problem, care should be taken to carry out husbandry activities from the same part of the enclosure as the public have access to, so that one end of the pen is free from human disturbance; this may give the cranes an area of their pen in which they feel more secure. (P87.7.w5)
    • Some cranes may be disturbed by the onset of artificial insemination prior to egg laying and not start laying. For such birds, avoid AI until after the first egg of the season has been laid. (P87.7.w5)
  • Egg searches should be started before the expected date of egg laying. However, It is important to carry out egg searches in a way which minimises disturbance to the cranes while maximising the chance of eggs being found as soon as they are laid. If possible, searches should be carried out from outside the enclosure. (B115.2.w7)
    • Some cranes will not lay eggs if personnel keep entering their enclosure to look for eggs. (B115.2.w7)
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Infertile Eggs and Failure to Hatch

Infertile eggs and poor hatchability may be produced due to wide variety factors, such as incorrect diet, incorrect pairing, incorrect flock size, environmental factors, disease, stress, disturbance and inbreeding.

Specific factors include:

  • Genetics: Birds which are inbred or of poor stock may produce a high proportion of infertile eggs.
  • Age: Fertility may be low in young birds. Males may not be fertile at an age when females may lay for the first time. Fertility may also be low in elderly birds, although fertile eggs have been produced from quite old birds (females and males).
  • Nutrition: Feeds which enable eggs to be laid nevertheless may be low in essential nutrients required for fertility and/or embryo development.
  • Pairing: Apparent pairs may be formed from two female birds, for example due to incorrect sex determination or incorrect assumption of gender. "Pairs" of birds formed in captivity may not be sufficiently compatible for mating to occur, even if they appear to be sharing an enclosure amicably. In some species a certain amount of dominance of the male over the female is required for successful mating. 
  • Courtship may be important to synchronise the breeding cycles of a pair of birds. N.B. Birds of the same species and subspecies, but originating from different locations, may show subtle differences in behaviour and reproductive physiology resulting in poorly synchronised reproductive condition between the male and female.
  • Flock effects: Depending on bird species, the stimulation of other birds of the same species may be required for maximum stimulation and fertility. Conversely, in territorial species the presence of other birds of the same or similar species may cause excessive territorial behaviour such as patrolling boundaries, and reduced mating activity.
  • Physical problems in mating: Foot problems such as bumblefoot or crooked toes, leg problems and wing problems may make effective mating difficult or impossible. Obesity, cloacal papillomas and, in birds with a phallus, phallus injuries may also interfere with mating.
  • Disease: Diseases may affect fertility in a variety of ways. Chronic diseases such as aspergillosis or avian tuberculosis may cause reduced fertility before overt clinical signs become evident. Internal parasites may result in debility directly or via a decrease in essential nutrients being absorbed by the host. External parasites cause irritation, general disturbance and sometimes blood loss.
  • Environment: A poor general environment is not conducive to maximum fertility. Specific environmental cues may be important, such as daylength or rainfall. Unhygienic environments also promote the development of diseases which may affect fertility. Enclosures lacking in important features such as cover, appropriate perches or appropriate nesting facilities may be associated with poor fertility.
  • Stress: Stress may be associated with a wide variety of factors, including enclosures which are inadequate in size or furnishings, excessive disturbance due to humans or predators outside the enclosure, vermin within the enclosure and intra- or inter-specific competition.
  • N.B. The features of the environment and interactions with other birds which are most important for fertility vary between species.

(J8.17.w1, J23.29.w1, B12.5.w10, B42, B105.15.w2, B106, B115.4.w1, B438.8.w8, N1.89.w1,P3.1995.w1)

  • In addition to infertility, eggs may also fail to hatch due to death of the embryo at any time from laying to incubation. Genetic factors, nutritional factors, viral, bacterial or fungal disease, exposure to a variety of toxins (e.g. oil, polychlorinated biphenyls, carbon monoxide) or incorrect conditions and handling during egg storage and incubation (e.g. temperature, humidity, turning, ventilation) may all affect hatchability. Death may occur early in development (see: Early-Embryonic-Death), mid-incubation (see: Mid-incubation Embryo Death), late in incubation (see: Dead-in-Shell) or during hatching (see: Hatching Problems) (J23.29.w1, B11.11.w20, B12.5.w10, B37.x.w1, B42, B106).
Waterfowl Consideration
  • Pairing of two female birds must be considered as a cause of persistent infertility. Such a pair may have been set up due to incorrect sexing and is most likely to be set up with monomorphic species. See above: Determining Sex
  • As with other animals, inbreeding in waterfowl may result in infertility.
  • Most waterfowl mate in the water. Lack of sufficient water may result in infertility.
  • Male waterfowl with injury to the phallus may be unable to mate successfully.
  • In some waterfowl, such as many of the pochards, group courtship activity is beneficial. In highly territorial geese, swans (and some ducks), physical and visual separation may be required for maximum fertility. Shy species may benefit from separate enclosures in which they will not be disturbed by other birds; if they are in mixed-species enclosures these should be sufficiently large and with ample cover and a variety of ponds. Lone males may need to be removed from mixed-flock enclosures to avoid their interfering with paired birds.

(J8.17.w1, B29, B106, V.w5).

Crane Consideration
  • Infertility may be associated with poor semen quality, mechanical problems making copulation difficult for pinioned or tenotomised birds, and behavioural problems. (J54.2.w1)
  • Not all "pairs" of a male and female are properly sexually compatible. (P92.1.w6)
  • Male cranes will produce semen without being paired (unlike females which generally will not lay eggs if unpaired). (B115.3.w2)
  • Infertility will result if two females are mistakenly kept as a pair (P92.1.w6). See above: Determining Sex
  • Production of fertile eggs may be reduced in pairs in which the female, rather than the male, is dominant. (B105.13.w4, P76.1990.w2)
  • Pinioned males may be less able to mount the female successfully for copulation, resulting in reduced fertilisation of eggs. (J23.17.w5)
  • Eggs will be infertile in pairs which are kept separated by a fence due to excessive aggression by the male, unless artificial insemination is used. (P87.8.w1, V.w5)
  • Note:
    • Fertility can be increased by using artificial insemination. (J54.2.w1) See below: Artificial Insemination
    • In some cases, pairs which have persistently produced infertile eggs, have copulated successfully and produced fertile eggs after being allowed to incubate, hatch and rear offspring. (P92.1.w6)

Sperm storage and the "fertile period"

  • Female cranes may continue to produce fertile eggs for some days after natural or artificial insemination. In experiments where fertile pairs of Grus grus - Common crane were placed into adjacent enclosures (i.e. physically separated, fertile eggs were laid six and ten days after separation. (P87.4.w2)
  • Artificial insemination records indicate nine days from insemination to laying of fertile eggs and records at PWRC indicate one female Grus canadensis - Sandhill crane laid a fertile egg at least 20 days after artificial insemination; this bird was housed with a male, but no fertile eggs had ever been produced from the pair without the use of artificial insemination. (P87.4.w2)
  • Fertile eggs have been produced from up to 16 days post-insemination in Grus carunculatus - Wattled cranes. (P87.7.w4)

Critical point

  • It appears that artificial insemination is unlikely to result in fertilisation if it occurs less than 2.5-3 days prior to oviposition. In cranes, oviposition occurs about 56-60 hours + after ovulation. (P87.7.w4)
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Control of Egg Production

  • In the wild many species of bird lay, hatch and rear a single clutch in a season. However, many species will re-nest if the clutch of eggs is destroyed or sometimes if the chicks are lost early in the rearing period. This potential for re-laying is exploited in aviculture, with clutches of eggs removed to stimulate the production of more eggs. In some birds it is possible to increase the total number of eggs laid in one clutch by removing eggs as they are laid.
  • It is important to remember that producing more than one clutch of eggs places a greater physiological strain on the female and that appropriate feeding, including provision of calcium, must be maintained throughout the laying period.

(J23.29.w1, B42, B96, B115.3.w2, P1.1977.w2)

Waterfowl Consideration
  • Most waterfowl, if left to sit, hatch and rear their own offspring, will lay only one clutch of eggs per year. Egg production may be increased by removing eggs, either as they are laid or (particularly for geese) when the clutch is completed. This is particularly useful to increase the production of eggs from rare or economically important species.
  • If eggs are removed as they are laid, one or two dummy eggs should be left or the female may desert the nest as being "unsafe", due to the constant "predation". Eggs should be collected when the female has left the nest; a bird which is disturbed at the nest may not return to that site to lay the rest of the clutch.
  • Destroying the nest after the whole clutch has been laid may assist in encouraging re-laying. Removing the nesting materials also reduces the build-up of contamination which may lead to bacterial or fungal infection of the eggs.
  • The second or third clutch may be left to be parent incubated and reared, if the enclosure is suitably fenced and protected against vermin such as rats. It is suggested that allowing the female to hatch some eggs (her own or otherwise) may also prevent females stopping laying due to the whole enclosure being unsafe from "predation".

(B7, B37.x.w1, B95, B97, P3.1987.w1).

Crane Consideration
  • Cranes are indeterminate layers and may lay again if their eggs are destroyed. In captivity, this characteristic can be used to increase egg production: if eggs are removed, either once each egg has been laid, or after the clutch (two eggs in most species) has been completed, often they will re-lay. (D437, J23.14.w5, J23.17.w5, P91.1.w6, P92.1.w6, P96.1.w1)
  • Note: It is essential to ensure a good quality diet and an excellent supply of calcium for breeding cranes, particularly if females are to be encouraged to produce addition eggs over the normal number; females cranes will eat more feed and more oyster shell (for calcium) while producing eggs. (B115.3.w2)
  • Some reduction in survival to fledging may be seen for later eggs. (N1.100.w)
  • Extended egg production may lead to calcium depletion, post-laying collapse, reduced fertility or hatchability and chick growth rate and survival. (B115.3.w2)
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Artificial Insemination and Cryopreservation

  • Artificial insemination (AI) has proved to be a useful tool for increasing fertility in a variety of birds where natural copulation is difficult due to body size differences, injury or deformity, or aberrant behaviour, as well as to transfer semen from males to females at another location or in a different pen. Methods used for semen collection include cooperative, massage and electro-ejaculation techniques.
  • Cooperative collection of semen is commonly used with sexually-imprinted raptors, with the male bird encouraged to copulate with some form of "dummy", and deposit semen in or on a suitable receptacle. The female is encouraged to assume a copulatory position and the semen is deposited in the cloaca or the everted oviduct.
  • The massage technique has been used commonly with domestic poultry, with an assistant holding and massaging the bird while the operator massages the cloacal area and collects the sample, or inseminates the female.
  • Electroejaculation has been used by researchers in, for example domestic ducks and geese, and some psittacines.
  • Semen collection by massage is most likely to be successful if the bird is not stressed by the catching, handling and massage procedure.
  • The volumes of semen which may be collected from a bird are very variable, but frequently small.
  • After insemination (whether natural or artificial), semen may be stored in sperm host glands at the uterovaginal junction. If possible, semen is inseminated into the oviduct, allowing semen storage; satisfactory results may also be obtained from insemination into the cloaca, but more frequent inseminations may be required, timed closely to coincide with oviposition.
  • The frequency of insemination required depends on factors such as semen quality, duration of fertility, age and stage of egg production. Several repeated inseminations prior to the onset of egg production may improve later fertility.
  • Semen characteristics such as volume, concentration of sperm, percentage of live sperm and percentage of progressively motile sperm may be evaluated. However, the most reliable test of viability is the resultant production of fertile eggs.
  • Semen may also be stored within a cryoprotectant, dimethylsulfoxide (DMSO), frozen at -196 C in liquid nitrogen.
  • N.B. Artificial insemination is useful only if the female is laying eggs and should be seen as an adjunct to other management practices which may increase natural fertility, including considerations of enclosure design, behavioural requirements, specific environmental cues, mate choice and nutritional requirements. AI is labour-intensive and time-consuming; other means of correcting infertility should be considered prior to the use of AI.
  • Artificial insemination, together with cryopreservation of semen can assist reproduction of individuals with behavioural or anatomical handicaps to natural mating, improve reproduction of genetically important individuals, facilitate the exchange of genetic material between populations, including between in situ and ex situ population as well as between ex situ populations, and enable preservation of genetic diversity, providing insurance against genetic loss. (B445.w4)

Cryopreservation

  • Cryopreservation allows sperm to be shipped between collections over long distances, and between in situ and ex situ populations, and to be preserved for long times. (B445.w8, P1.1980.w6)
  • It may be useful particularly to preserve semen from males with important genetic backgrounds (e.g. founders) for use in future generations, to maintain genetic diversity and equalise genetic contributions to the gene pool. (B445.w8, P1.1980.w6, J312.18.w1)

(B105.14.w1, J312.18.w1, P1.1980.w6, P17.43.w1, V.w5).

Waterfowl Consideration
  • The semen volume which may be collected from a duck is approximately 0.2-0.4 mL, with a concentration of 2.0-9.0 x 109 spermatozoa per millilitre of semen. Insemination may produce fertile eggs for 8-16 days. From a goose, 10-800l (microlitres) may be collected (B105.14.w1).
  • Usually, the phallus of waterfowl is everted during semen collection, with semen being collected from the base and tip of the phallus with a small funnel, tube or suction device. It is important to ensure that the phallus is not injured by rough handling during semen collection. It may be possible to collect semen by gentle manipulation of the vent without everting the phallus. This may reduce the risk of injury and also loss of semen spread over the surface of the phallus.
  • A massage technique is usually used for collection of semen from waterfowl, although electroejaculation has also been used. Insemination into the oviduct is preferred, but insemination into the cloaca may also be used.
  • Fertile eggs have been produced using frozen goose semen (Branta canadensis leucopareia - Aleutian Canada goose), with approximately 50% of live spermatazoa surviving the freeze-thaw process. Commercial poultry extender was used, adjusted to 270 +/- 30 mOs and pH 7.5+/-0.4, and with the addition of dimethylsulfoxide (DMSO) to a concentration of 7%, which produced 19 fertile eggs out of 31. The use of clean semen, stored at 1C-5C before freezing and frozen in 7% or 8% DMSO was suggested, with a note that the equivalent of three ejaculates should be used for insemination after freezing, storage in liquid nitrogen and thawing in an ice bath (J54.9.w1).

(J54.9.w1, B13.46.w1, B105.14.w1).

Crane Consideration

Crane AI, stroking male crane. Click here for full-page view with caption. Crane AI. Collecting from the male. Click here for full-page view with caption. Crane AI. Collecting from the male. Click here for full-page view with captionCrane AI. Collecting from the male. Click here for full-page view with caption.Collecting crane semen off a shot glass. Click here for full-page view with caption. Checking the female crane ofr an egg before insemination. Click here for full-page view with caption.  Stroking a female crane for AI. Click here for full-page view with caption. Stroking a female crane for AI. Click here for full-page view with caption. Crane semen sample with high sperm count. Click here for full-page view with caption. Cryopreservation tank. Click here for full-page view with caption. Cryopreservation tank, open, showing straws. Click here for full-page view with caption.

In the wild, cranes start copulation 20-30 days before the onset of egg laying, and will copulate several times a day. (P96.1.w1)

Artificial insemination is an extremely useful tool to improve fertility in cranes.

  • It is particularly useful when natural copulation is not occurring, because:
    • Loss or all or part of a wing (e.g. due to pinioning), or injuries to the legs or toes make it more difficult for the male to mount and balance properly for natural mating;
    • A pair of cranes have to be maintained side by side rather than in the same pen, due to aggression;
    • A crane is imprinted onto the wrong species (e.g. humans) and will not pair with his/her own species.
    • There is a shortage of unrelated sexually mature males to pair with available females.
    • A pair of cranes is not copulating due to the presence of inhibitory factors such as disturbance.
  • For genetic reasons, when insemination with a male other than the the female's mate is required.
    • e.g. increasing the genetic influence of a given male on the population by using his semen to inseminate several females.
    • insemination can be carried out when the male and female are at geographically distant locations from one another.
    • Note: this avoids the need to break and reform pair bonds. 
  • To increase female fertility, by inseminating with semen from several males.
    • Note: it is then necessary to determine paternity by special tests. (B115.11A.w10)

(B115.11A.w10, P87.8.w1, P90.1.w2, P91.1.w6, P96.1.w1, N1.86.w2)

  • Artificial insemination also can be used for creation of hybrid cranes for specific research purposes. (B115.11A.w10)
Note:
  • Conditioning of the male crane to AI before egg laying is expected is advantageous to ensure the male is producing semen by the time the female lays eggs. (B115.2.w7)
  • Collection of semen for artificial insemination does not appear to reduce natural fertility. However, a male which is successfully naturally copulating may not produce good semen samples during semen collection, due to depletion of semen reserves. (P87.8.w2)
  • Artificial insemination is time-consuming and labour-intensive, requiring repeated catching and handling of the birds. It should not be used unnecessarily. (P1.1980.w8)
  • Good record keeping is extremely important. (N31.33.w2)

Factors affecting the effectiveness of artificial insemination

  • A study of cranes of ten species at ICF indicated that fertility rates when artificial insemination was used increased significantly (p<0.05) with: (P87.7.w4)
    • higher sperm motility; (P87.7.w4)
    • higher sperm density; (P87.7.w4)
    • inseminations in the period 4-7 days before oviposition (highest with two inseminations in this period, lowest with zero). (P87.7.w4)
  • In general, artificial insemination is most effective if carried out three times a week. However, there are species-related and individual variation; ideally, within a basic plan, insemination times should be tailored to the individual birds. (P87.7.w4)
    • Fertility is reduced if insemination is carried out more than eight days before oviposition or less than 2-3 days before oviposition. (P87.7.w4)
      • Insemination must occur at least 56-60+ hours before oviposition, before the formation of the shell membrane. (P87.7.w4)
    • Fertility for subsequent eggs is higher if insemination is carried out within a few hours after oviposition rather than 2-3 days before oviposition. (P17.43.w1)
    • Within a schedule of three times per week, insemination times should be adjusted based on the next expected laying date for a given female. (P87.7.w4)
    • Some whooping cranes at ICF delay the start of egg laying, or stop laying, if inseminated more than twice per week. (P87.7.w4)
    • In wattled cranes at ICF, 60% fertility was obtained if insemination had been carried out 4-16 days before egg laying. (P87.7.w4)
    • Some pairs (of various species) may be disturbed if AI is carried out early in the breeding season and may not start laying. For these pairs, AI should be started only after laying has started. (P87.7.w5)
  • For good fertility, 15-20 million sperm are required per insemination. (B115.11B.w11, P91.1.w4)
  • The best fertility is seen with 200 million sperm per insemination. (J54.2.w1)
  • Male cranes vary considerably in their individual semen quality and quantity. (P92.1.w1)
    • Effects of age
    • Effects of season: 
      • Dates and duration of semen production appear to correlate with times of normal breeding in the wild. In general, duration of semen production is longest in the tropical species, shorter in the temperate-breeding species and shortest in the Arctic-breeding species. Dates noted include: Grus japonensis - Red-crowned crane early March to early/mid June (correlates with wild breeding season), fertilisation early March to late June (wild mid-April to mid-May), Grus leucogeranus - Siberian crane early April to late May (with extended photoperiod lights; duration of semen production shorter than in other cranes) (wild late May to early June); eastern sarus (Grus antigone - Sarus crane) and Grus rubicunda - Brolga May to August (wild in Australia, December to February). (P92.1.w1)

Cryopreservation

  • Cryopreservation can be used to preserve the founder gene pool of endangered cranes, as well as to allow insemination of females if semen production and egg laying are asynchronous, and for shipping of semen long distances (allowing genetic transfer without moving the birds). (B115.11B.w11, J40.49.w2, P91.1.w4)
  • Only high-quality semen samples should be cryopreserved, and the equivalent of two to four ejaculates should be used for each insemination to compensate for loss of live sperm during freezing and thawing as well as losses of cells on the sides of straws etc. (B115.11B.w11, P91.1.w4)
  • Samples should be thawed immediately prior to insemination. (B115.11B.w11)
  • Cropreserved semen has been used successfully to produce four fertile Mississippi sandhill crane eggs, of which two hatched, in 2007 and 2008; both surviving to fledging. One was released at the Mississippi sandhill crane Wildlife Refuge in January 2008 "and continues to thrive". (P87.11.w9)
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Authors & Referees

Authors Dr Debra Bourne MA VetMB PhD MRCVS (V.w5)
Referee Suzanne I Boardman BVMS MRCVS (V.w6)

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